Bandit Mook

While it's pretty common for RPGs to give your party a thief as a team member, or otherwise give the player an ability to swipe goods off an opponent during battle, it is relatively rare to encounter monsters or foes that do the same thing to you, even when you're specifically fighting thieves as opponents.

Now enter the Bandit Mook.

This is the occasional Mook who isn't interested in your party's demise so much as he is in your Bag of Holding. He may have a share of normal attacks, but he's unlikely to do any serious harm -- his signature attack pattern is to swipe something from your Hyperspace Arsenal then disappear as quickly as possible, taking the stolen goods with him. Fenced goods may be gone forever if stolen, so for this reason he will (usually) interest himself only in items that can be easily replaced at local shops. After all, if the Bandit Mook randomly made off with your hard-earned MacGuffins and Plot Coupons, this could render your game Unwinnable By Design, and nobody wants that.

Defeating a Bandit Mook frequently results in the immediate recovery of any stolen goods; but this isn't always the case, especially if it was just cash. (Exactly how he can keep you from physically looting his corpse is a mystery, but then again, it may be because Everything Fades.)

The obvious exemption from this trope is if an item (important or otherwise) is stolen solely because the plot demands it, like the MacGuffin Delivery Service.

Compare Mooks Ate My Equipment.

Video Games

 * In Growlanser series, the imp and Catgirl enemies will steal items and gold from party members.
 * Akalabeth, the first adventure in the Ultima series, had a Thief who could steal any items your character had on him, and a Leprechaun who stole half your food each turn. In both cases, the goods became Lost Forever.
 * The Legend of Zelda Majoras Mask has the infamous Takkuri, a bird that not only steals rupees but also an empty bottle or even your sword. When this happens you have to go to a curiosity shop, whose owner is probably the owner of the Takkuri, and buy them back overpriced. As if weren't enough the Takkuri requires fifteen hits to be killed. On the other hand, once killed it leaves a rupee the value of two hundred normal ones. Note that you could always play the Song of Time to go back in time and regain your stolen stuff free of charge, but it's a little jarring to do that if you'd made a lot of progress on that particular day.
 * A Link to the Past had a thief enemy as well. While he never steals anything of great importance (just bombs, arrows, rupees etc.), he's 10x a bigger pain in the ass than the Takkuri by virtue of the fact that he can't be killed or even stunned.
 * Final Fantasy:
 * Final Fantasy VI had one enemy in Mt. Zozo, a bear whose primary strategy was stealing four digits of Gil, then suddenly fleeing on the next turn.
 * If defeated first, it returns the exact amount it stole. If Relm is in the party with her Cat-Ear Hood, he'll somehow drop twice what he stole (the Cat-Ear Hood doubles Gil drops.)
 * Final Fantasy VII had enemies that steal items from you, including accessories. You could get them back if you killed them fast enough. If.
 * The Final Fantasy Tactics series have Thief as a job/class for human units and were usually the first targets players went after other than the White Mages. Aside from being very fast and having high evasion, enemy thieves, like your thieves, can steal money, items, and equipment, which could lead to a Lost Forever if an enemy thief stole a unique piece of equipment. In Final Fantasy Tactics a 2, thieves got nerfed and can only steal pieces of loot, money, and certain equipment types.
 * Nethack had Leprechauns who stole gold, and Nymphs who stole items before teleporting away. Nymphs, in particular, could steal without limit, they could use the stolen goods against you, and some of them were even invisible.
 * Paper Mario had Bandits in Dry Dry Desert, who stole coins from Mario with each attack, fleeing the battle on the next turn. Attacking them made them drop the loot, with Mario recovering it immediately.
 * They return in the sequel as common enemies, some of which can steal items and even badges, and must be defeated to regain your stolen loot. They also appear as neutral NPCs.
 * Gauntlet has the Thief, who steals treasure or, if possible, a potion from a player (selected randomly if two, three or four are playing). They also love to infuriate their victim by running away at lightning speeds proclaiming "YOU CAN'T CATCH ME!" in primitive digitized speech.
 * Some Kirby games, like Kirby Super Star, have TAC, who can steal your power -- or outright kidnap your partner.
 * Thieves in the Fire Emblem series can usually unlock and loot chests if you don't get to them quickly enough, and will them promptly make off with the goods if you don't kill them before they leave the map. Sometimes they'll perform other acts of banditry, and aim for nearby villages instead which usually have gold or useful items if you warn them to shut their gates. Depending on the game, the thieves may or may not be able to steal items from your slower characters.
 * Yoshis Island had the same Bandits from Paper Mario that steal Baby Mario from your back and run off with him as he screams and the timer goes down. Luckily they can never fully run away. Frogs and weak Toadys also do it too.
 * Shin Megami Tensei Strange Journey presents Macca Beam, an enemy-exclusive skill you'll run into as early as Sector B, which forces the target to drop a fraction of the team's Macca and has an extremely high accuracy rate. Then the final sector introduces Wastrel Beam, which drops an even larger percentage of money. Macca is just "energy" in this game, so killing the enemy won't give it back. Very often, players will just reload from an earlier save than go to the trouble of earning back all the money lost.
 * Septerra Core has a few thief/pirate/miscellaneous thug mooks, which have an attack that damages your funds rather than health. Of course, they would have to do it several times in one battle to cancel out your victory spoils.
 * The uber-annoying Thief Bot from Descent are these types of mooks. They attempt to sneak up on you, often while you're in a pitched firefight with other enemies, and steal your weapon upgrades and missiles. Often while you're in the middle of using them. They are quick, require about six or seven times the firepower to take down as a normal mook, and have a habit of dodging your shots, and if they were carrying something they lifted from you when they die there's a chance it could get blown up.
 * The various groups of Bandits, Sea Raiders, Looters and Deserters in Mount and Blade play with this trope a little. You get a chance to beat the living hell out of them first, but if you do lose to them in battle then they take you prisoner, and will quite happily relieve you of things in your inventory: spare weapons, spare armour, your actual weapons, your horse, party members, quest items. Annoyingly, even though the quest items they may actually steal are pretty common and easy enough to pick up in any village, you will fail the quest if they take them...
 * Spoofed in a Kingdom of Loathing April Fool's Day "sneak preview" with a Disco Bandit NPC. The preview also demonstrated an NPC special attack that would destroy all worn/wielded equipment. Subverted with the dirty thieving bandits; the game currency is meat, but they steal it from your hitpoints rather than your wallet.
 * Gremlins in the Exile series stole your food when they struck you. They also didn't give it back when they died, presumably thanks to some kind of fey magic.
 * Super Mario 64 had Klepto the Condor in Shifting Sands Land and Tiny-Huge Island, who steals your cap.
 * Super Mario RPG, the first Mario role playing game, had Croco the crook.
 * One of the first enemies you meet in Earthbound Zero, the Crow, steals food items and does not return them upon death.
 * The Spiteful Crow from Earthbound, again one of the first enemies that Ness meets, is also fond of stealing your food.
 * The Smirking Thief in Castle of the Winds can steal your money or whatever's on your belt, then randomly teleport to anywhere else in the level. Very agile and requires three fireballs worth of damage to kill. You can get your stuff back if you can find and kill it.
 * Minecraft introduces the Endermen, a tall and sleek mob that is passive unless provoked by attacking it or looking at it. When they are not provoked, Endermen will wander aimlessly and may steal a block and place it somewhere else (such as dirt, grass, sand, gravel, mushrooms, flowers, etc.). This is usually of no concern if you are exploring but if you have a structure built by your own hands, things can get nasty if Endermen start to pick apart your structure, depending on how you have things set up. While Endermen can only take 1 block at a time, the block is Lost Forever once an Endermen steals it, even if you kill it.
 * However, as of 1.0, Enderman can only pick up some natural materials like dirt, sand, and gravel (except for TNT), making it much easier to deal with them.
 * Chrono Trigger has rats in Lab 16 who will steal a tonic from your inventory and run away if they manage to catch you.
 * The Meta-Being known as Gliro in Baroque likes to steal an item from your inventory, then flee at top speed. And yes, it can snatch the sword right out of your hands or the coat right off your back. If you manage to chase it down and kill--er, purify it, it will drop whatever it stole from you...but sometimes the Gliro chooses to throw the item at you in self-defense, in which case the item will be Lost Forever.
 * Pokémon Ruby and Sapphire introduced Mons that learn item-stealing moves naturally, such as Linoone (with Covet), potentially making them Bandit Mooks. As well as item-disabling moves like Knock Off. The Generation IV games took it up a notch with moves like Pluck, which damages the enemy and eats any berry the target is holding.
 * The Packrat in Anvil of Dawn.
 * The original King's Quest has the Dwarf, who steals whatever treasure you're carrying. If this happens, the game becomes Unwinnable.
 * The gnomes in the Harry Potter video games would steal a few of your Bertie Bott Every Flavor Beans if they ran into you. They weren't reobtainable in the first game, but they were in the second game.
 * Kid Icarus featured Pluton - who made matters worse by being invlunerable on top of everything else. They return in Kid Icarus Uprising, where they thankfully can finally be destroyed.

Other

 * In the card game Munchkin a lot of different Bad Stuff steal and/or destroy the player's equipment. A double-edged sword because it has no effect if you have no equipment of that kind, but very irritating if you do.
 * In the board game Afrikan tähti, there's a round cardboard disc facing downwards on each location space. Landing on a space that still has its disc, you can either choose to pay or try your luck with the die to claim it. Three of these coins are Bandits: they steal all of the player's money. No buts. This could leave you on an island, and yes, travelling by ships costs money, meaning facing a Bandit on St. Helen or Madagascar was practically an instant game-over. House Rules were needed to fix this until decades later, new printings featured rules that featured an official solution to the problem.