Game Breaker/Video Games/Role-Playing Game/Shin Megami Tensei

In General

 * Fusion in general can get you some hilarious results in either Persona 3 or 4. Skill inheritance can get you a persona with all 3 full-party autobuff skills by mid-game. Most encounters won't survive 3 turns of physical attacks if a player uses debuffs as well.

Shin Megami Tensei

 * Shin Megami Tensei I has the Zio line of skills,stun almost everything in the game. With high enough speed, the heroine can immobilize pretty much everything before it even has a chance to move. The Bufu line of spells works just as well, but you need demons for those.
 * In Shin Megami Tensei II, it's damage and defense buffs and debuffs, which stack with themselves and last until they are dispelled, something that not every boss is capable of. But more-so is the Divine Retribution spell. It tears off a quarter of of an enemy's health with an alignment opposite to to the spell's caster, and it works on bosses with no reduction.
 * Speaking of stackable stat buffs, there is a passive Game Breaker that can, if one is not averse to Level Grinding and item farming, turn your main character into a stat buffed tank. This is achieved by farming gemstones from demons until you have nine of each type, whereupon stats buffs are applied to your permanent stats as long as you don't reduce the gemstone count, and this condition is stupidly easy to honor, since the only two ways to lose gemstones is to spend them as currency at a certain store (which can make the game easier for some gamers but never need be visited) or use them as trade items in demon negotiation, which, again, need not be done because all demons can be bribed with other materials. This doesn't mean that the stat buffs make passing the skill check for the bonus dungeon easier (the check goes by your natural skill level, ignoring buffs), but this can be used to make certain story event skill checks effortless.
 * In Shin Megami Tensei If. Having save data from other Atlus games when you reach the Appraisal Shop in the World of Sloth will get you 18 extra stat points(effectively letting you reach level 117 in a game with a 99 max), increases all of your demons' HP permanently by 25%, gets all of the buff spells on your partner, Sabbatma, and ten somas. That's ten party-wide full-HP and MP healing items, a spell that lets your partner summon demons, and the three most useful spells in the game!
 * Shin Megami Tensei Nocturne has its fair share of Breakers too, in many forms. Masakados, for example, nullifies just about every attack on you and increases strength, vitality, magic and agility by 10 (the max on stats in this game is 40). Its abilities are also ridiculously powerful; first is Megidolaon, then a very powerful Expel-type move, and then the ability to reflect all elements and physical moves.
 * Most of these abilities, though, aren't as powerful as they might seem --- first of all, by the time you can acquire Megidolaon, you are probably already at a fairly high level, reducing its damage considerably (magic damage, unlike physical, decreases with levels). Second of all, the Expel-type move only deals damage, which has very few, if any, practical uses. Finally, physical reflection is pretty much the only useful reflect skill of all, as enemies who already use spells are extremely likely to be at least resistant to (or, at that point, actually absorb) the element they cast.
 * Then there's Fog Breath, which drops the accuracy and evasion of every enemy by two stages and can't be blocked. You can get this skill from a common Magatama as early as Level 21, and although the MP cost is steep at that level, Fog Breath retains its value right up until the endgame.
 * God's Bow and Hell Gaze are basically the same attack, just with different elements (Bow is Expel, Gaze is Death); Either they can block that element, or they die. Simple as that.
 * Hoo boy, Black Frost. Where to start? He's one of two demons (the other being ) that can be recruited regardless of your level; outside of New Game+, that is, he has ridiculously high stats, comes with a Ma-Dyne spell, and has no weakness. And his resistances? He absorbs ice, reflects fire and darkness, is immune to light, and takes negligible damage from physical attacks. This means the only attacks effective against him are electricity and force.
 * Atropos, when you get her she has Element Boosts, which amp up damage of a specific element by 50% In other words, she is optimal for being a Quad dyne spell user.
 * Daisoujou. Immune to every status ailment in the book in some way, has good Magic stat, and can restore its own HP and MP during boss fights with Meditation, which makes him a stellar support caster if you give him Prayer, especially if you sacrifice demons to level him up.
 * Recarmdra, with proper exploiting and fusion, you can create an infinite cycle of healing or one powerful mage. When the HP/MP of your party is low, have that demon use Recarmdra, Blammo; your party gets back all their HP and MP, next have another demon use Samrecarm to resurrect it, and summon it again. Mana Drain also is useful, give it to a powerful magic user and let them do all the damage dealing; it is even better if they know Megido class magic.
 * Shin Megami Tensei: Strange Journey has Victory Cry + Jihad (or any powerful Almighty-type spell) on a demon. The Eternal Rest spell in conjunction with any sleep spell is also effective, as status ailments work quite often on a surprising amount of enemies, and the combo can lead to a near Disc One Nuke if you get it early enough.
 * There are several guns that allow you to cause the Stone element. This counts as instant death. Almost everything except bosses are weak against this attack. Your Main Character gains 4x the EXP he would normally get if you have no demons out. Manshonyaga (an early game weapon with the stone element) will allow you to gain levels every 2-3 fights for a while.
 * The 4x EXP bonus can also be gotten by softening up an opponent with your demons then giving them the return order and finishing the battle on your own. This makes it trivial to break the game in a different way.
 * While Jihad is commonly considered the ultimate skill, it isn't necessarily the most damaging. That falls to the ultra-rare skill Desperate Hit (only naturally on Demonee-ho, and can only be passed on via demon source), which does a random number of almighty hits. If it does 3 or more to a single enemy, that enemy takes more damage than it would from Jihad. VERY useful agaist bosses. Not to mention it's only 40 mp.

Persona 2

 * In Persona 2, Lucifer and Satan had a spell, "Alpha & Omega" which skipped the damage numbers and just wipes out the enemy party. Only two bosses in the game actually had some sort of countermove for it. One is an enemy that is immune to all attacks until you remove its barrier, and the other is Philemon, who will reflect the attack on YOU and cause a Total Party Kill.
 * Before this are the spells Hell Desert, Megalo-Fire, Storm Nightmare and Maelstrom. It's technically a Total Party Kill that can only be avoided by one of two means; luck (as these spells are ungodly accurate) or resistance to a certain element (in respective order; Earth, fire, water or wind). These spells are available even earlier than Trimurti, however.
 * What is game breaking is Eikichi's ultimate weapon, the Supernova, in Persona 2: Innocent Sin. Not only is it the most powerful weapon in the game, but you can also get it very very early. It allows you to mow through the first half of the game and some of the latter half with extreme ease. Downside is, it's an extremely difficult weapon to get.
 * One broken spell combo is "Trimurti" by the personas Shiva, Vishnu, and Brahma. It will KO all non-boss enemies. It is more broken since these three can be obtain far earlier than Lucifer and Satan and do not require the insane MP consumptions. This only applies to Innocent Sin since it was nerfed in Eternal Punishment.
 * Pegasus Combo might not be that Game Breaker, but being able to deal about 400 damage points since level 10 is something to consider.

Persona 3

 * In Persona 3, the Lucifer (or Helel in the remakes) persona (in addition to being the most powerful persona on its own, bar none) gives access to "Armageddon", a spell that deals 9999 almighty damage (cannot be blocked or absorbed) to all enemies at 100% accuracy. While it will kill every non-Bonus Boss enemy in the game, Armageddon in itself isn't a Game Breaker, because it costs 100% of your MP to cast. No, what makes it a Game Breaker is that another of Lucifer's abilities, "Victory Cry", replenishes all your HP and MP at the end of each combat. End result: You win everything.
 * To add insult to injury, it's fairly easy to give Lucifer the "spell master" ability, which halves all MP usage. Yes, that includes Armageddon. Now, even going into combat in less than 100% shape lets you win everything as well.
 * It was nerfed in the sequel, a little--Lucifer (now Helel) no longer learns Victory Cry naturally, and one might argue that it can be a pain to get it on the fusion components.
 * What!? Lucifer is still in the game, part of the Judgment arcana now though. And he IS a fusion component for Helel, meaning it is absurdly easy to get Victory Cry on Helel, thus becoming an unstoppable snowball once again.
 * Outright removed in Portable, where Fusion Raids are done via items that require grinding for items (and Armageddon requires 99 of the main item and 10 of a hard to get one).
 * However, Portable brought a new Game Breaker to the table: Skill Cards. Think TM's from Pokémon, only 1) you can easily farm them and 2) there are no restrictions to what persona can learn what skill from cards. This means you can get personas with skills that they couldn't have through fusion (ex a Fire type casting Bufu spells). While it doesn't have the unique, superpowerful skills (Morning Star, Black Viper, Die For Me, Thunder Reign, Ragnarok, stuff like that), it does have the "Absorb x attribute" skills. This makes it trivially easy to cover up weaknesses in strong personae. This can be taken to Nigh Invulnerable levels with a Beelzebub that essentially Blocks, Absorbs or Repels every attribute (and still have slots for attacks!).
 * Also of note: Skill Cards can be reproduced for no cost. The Inari Sushi in the temple can take one card and make a copy of it after a few days. If you religiously go there every time he finishes, you can load up on very powerful skills you can put on any Persona you want.

Persona 4

 * Though spell combinations weren't included in Persona 4, Lucifer makes his return as the notoriously hard-to-fuse but gloriously broken ultimate Persona of the Judgement arcana. He learns both Victory Cry and Spell Master naturally and tears up Shadows like nobody's business. Even more broken (and even more of a pain to get) is the game's sole Persona of the World arcana, Izanagi-no-Okami. This one starts with Victory Cry as a base skill, and proceeds to learn 4 high-level elemental skills and an amping skill for each one. He is a bit Awesome but Impractical, because he doesn't inherit any skills, and has no immunities nor any protection from Insta Kill Light and Dark spells.
 * Trumpeter, on the other hand, starts off Immune to Dark, Reflecting Light and Electricity, and Absorbing Ice. As a Hexagon fusion, it is moderately easy to get the other three immunities, giving you a person immune to everything except Almighty and Poison. On top of that, Trumpter gets the best buff and debuff spells and the strongest non-unique Almighty spell automatically.
 * What happened to Yoshitsune? Power Charged Hassou Tobi DOUBLES the damage output of a Power Charged Primal Force, the second-strongest physical attack in the game. Not to mention no weaknesses, and Yoshitsune is one of the most customizable Persona in the game (he only needs Power Charge and Hassou Tobi, and you can technically get Power Charge off of a slave), meaning you can have a semi-invincible god slaughtering the field.
 * Beelzebub in Persona 4 is the ultimate tank Persona. As long as you give it something to counter physical attacks, then the only thing it won't absorb, nullify, or reflect is wind and light.
 * It is Painfully trivial (though time consuming) to get Null Light on Beelzebub in Persona 4, so the tankage continues!
 * Random skill changes can give you Victory Cry at Level 24. No, really. Kaiwan in P4 comes with Tetrakarn, which randomly changes to any other equivalent skill on certain days. A lot of Save Scumming can end you up with Victory Cry at a ridiculous level.
 * Not to mention that this Victory Cry can then be spread to other Personas. It's possible therefore to carry a Victory Cry slave throughout the whole damn game.

Other Shin Megami Tensei

 * The Null Attack skill from Digital Devil Saga nulls everything except Almighty attacks. This makes you effectively invincible for 90% of the game as only the last two dungeons have random encounters that make use of almighty attacks and none of the storyline bosses use almighty as their main form of attack. It won't help you against the bonus bosses though since they just love their powerful unique almighty attacks and the will rip you to shreds on his first turn if you dare to have immunities equipped.


 * In Devil Survivor, some skill combinations certainly count. Most notable, however, is Drain. It does Almighty damage (which means that 99.9% of enemies can't resist, null, deflect, or absorb it), is surprisingly damaging, and robs the enemy of their HP and MP while replenishing yours.
 * Also, Holy Dance and Drain Hit+Power Hit+Any Phys passive buff.
 * And also: Tyrant + Megidolaon + leader with Magic Yang = free one-turn kill every turn. And if you've got Awakening as well, even better!
 * Petra Eyes is extremely useful, at least on the first run, since petrified characters can be killed in one hit with luck no matter the HP or level. Being an Atlus game filled with Goddamned Bats where a huge part of them aren't resistant.
 * In the Overclocked remake, this is expanded with the combination of Makajamon + Grimoire + Death Call. Makajamon has a high natural chance of success (higher than Petra Eyes) but just mutes the enemy. Grimoire boosts the chance of status effects working. Death Call kills all muted/stunned enemies. The result? Instant death to anything that isn't immune to Curse/Mystic.
 * Pierce bypasses resistance to, nullification of, and draining of physical attacks, unless the demon's name starts with "Bel" and ends with "dr". Pair this up with Deathbound and you can demolish bosses that would otherwise make a physical assault hopeless, such as Belzeboul and.
 * Beast and Kishin demons on the same team. Beasts let you move again after you attack, and Kishins let you attack twice.
 * Even better, try Kishins and Vile / Dragon type demons. As long as your opponent doesn't have a demon of the same type, you can attack for two turns without the other team even touching you.
 * Vile and Dragon do come with a drawback though, of making your character wait longer between turns and reducing your Move (Viles have a higher attack range, but make you even slower). Still, that's not a big deal when you can attack twice in a row without ever being hit back, pretty much decimating whatever you're attacking.
 * In Devil Survivor 2 higher level Dragons get Evil Flow. One usage of this buffs your attack range to 6, allowing the player to attack anything shy of a few bosses with complete impunity.
 * The Multi-Strike skill introduced in Overclocked is a sterling example. Hits the entire enemy team with up to seven hits each depending on the user's agility. Stick it on a physical specialist with decent agility like Atsuro in or Hinako in the sequel and you'll quickly end up with a one-man/woman wrecking ball capable of completely decimating 95% of the enemy teams in the game.
 * Avians have Flight, which allows the team to teleport to their destination and ignore obstacles, boundaries, and enemy-occupied spaces in distance calculations, and yields an extra space of movement. This gains a lot of utility in the Belberith battle--normally, you have to use switches to enable a couple elevators so you can reach him, but with an Avian you can simply just fly across the pit without ever touching the switches.
 * Demikids Dark version Fusion system that affects only stats. While its not as unique as the Light version classic system, this is arguably better. With some easy work, and extremely abusable battle arena that gives out mid and high level demon as a prize, this allows you to Elite Tweak your party to ridiculous level.
 * The skill giving item. Oh gosh the skill giving item. Simmilar to Updated Rerelease of Persona3 this allows you to give skills to your demon, except your option in this game is limited to some exclusive moves instead of almost every moves in the game. The catch ? one of these items that is alvailable pretty early gives you 8 randomly hitting move that is alvailable to pretty much every demon in the game with fairly strong base power and sometime extra effect. This basicaly renders every other move barring healing move completely obsolete since you can spam this move to win any kind of fight. Combine with the fusion system above and even the Bonus Boss wont last more than one round.