Meritous

Meritous is an independently-made PC game, a cross between a top-view dungeon crawler and a bullet-hell shoot-em-up. In it, you control main character Merit, who travels through an enormous 3000-room labyrinth, the Orcus Dome, in order to find three artifacts called the PSI Keys, and restore them to their proper locations.

Although enemies fire copious amounts of bullets at you, you don't shoot back- instead, you have an attack called a PSI Circuit, which you charge up to unleash a shockwave that hits enemies and nullifies their shots. As you charge up the PSI Circuit, target reticules appear on nearby enemies, the circle indicating they're in range, and the cross indicating you've charged up enough to damage or kill them. You can't just use the PSI Circuit as often as you want, though. After releasing it, there's a cooldown time before you can charge up again, and the longer you charge up, the longer you have to wait. Destroyed enemies leave behind PSI crystals you can use to upgrade three facets of your PSI Circuit- Circuit Charge (charge up faster), Circuit Refill (less cooldown time), and Reflect Shields. When you have at least one level in Shields, a barrier is projected around Merit, which will deflect one bullet per shield level, before having to regenerate. As you upgrade Shields, the barrier becomes bigger, then shows multiple layers as it gets stronger.

Tropes used in Meritous include:

Beam Spam: On the Mook end, there's the first invisible enemy you encounter, as well as both circular ones. For bosses, there's Meradoca's 3rd and 4th forms.
Bullet Hell: Oh yes. If you don't think it's true, just wait until you reach a treasure room. Or a boss room. Or anywhere it wants to appear, really.
Deliberately Monochrome: The graphics are all shades and tones of one color, which shifts depending on where you are, and how many monsters are in the room. It's normally a light blue color, but if there's a lot of monsters in a room, the color may shift to gray, or even slightly red. When you enter a Treasure Room, things immediately turn red until the room is cleared. After the Point of No Return, it turns red and stays that way, becoming more saturated as you get closer to where the final boss is.
Dynamic Difficulty: Bosses become more powerful depending on your stats: higher shields prompt them to shoot more bullets, while faster Circuit Charge and Refill increase their health. Mooks shoot more bullets and gain better health with each boss you defeat.
Easy Mode Mockery: you can play the game in Wuss Mode, which makes things easier, but you won't get a proper ending.
Empty Room Psych: Averted. Chances are you'll be finding a lot of empty rooms and dead ends.
Infinity+1 Sword: The Agate Knife; you have to explore all 3,000 rooms in the game to get it. Once it's in your possession, it raises your stats above their normal maximum, and increases your health to six hits. It also allows you to fight the True Final Boss.
Invisible Monsters: There's quite a few of these, but once you have the Ethereal Monocle, they're represented by the question mark icon used to show enemies outside your current room.
Lost Forever: Averted, even with those little crystals. If you don't pick 'em up, the crystal machines scattered through the game will pull them into the room.
More Dakka: It gets especially insane during the boss fights. On the plus side, killing certain enemies also converts their bullets into crystals.
Multi Mook Melee: Whenever you enter a treasure room, the doors shut and numerous monsters start warping into the room in short bursts. Once you've beaten all the monsters, you get a ton of crystals, as well as some treasure chests which will contain either extra crystals, a free upgrade to one of your stats, or one of the upgrade items.
Nintendo Hard: It can vary where it starts, depending on how you boost stats, but things will reach this point sooner or later.
Oh Crap: Normally, the final boss spends a long time ranting at you about how you're apparently a huge asshole, nobody likes you, and that were stuck in the maze as a punishment (Which doesn't jell with the story according to the manual or history, but whatever). However, if you have the Agate Knife, he starts on his rant... then suddenly notices what you're holding and stops cold.
- Also, you will inevitably have this reaction, when the screen fills with bullets.
Point of No Return: Once you obtain the Cursed Seal, all the doors to rooms you haven't already entered disappear, save for those leading to labyrinth's entrance. Remaining monsters become Goddamned Bats—some with eight forms—able to move dangerously fast and fire an intimidating amount of bullets. On the plus side, they drop many more crystals than standard enemies.
Respawning Enemies: Averted. There's a limited number of monsters in the entire game, and the heads-up display even shows you the total, as well as how many you've killed.
That One Boss: Meradoca, lover of Beam Spam that it is. It's also the only one of the artifact-room bosses which has more than three forms.
True Final Boss: The aforementioned version of Wervyn Anixil, if you got the Agate Knife. He has three phases, each of which is extremely difficult even with your newly maximized stats and six hits (which, might I add, are replenished after you beat his second phase). During the third phase, the screen turns a psychedelic green and starts cycling through tones of it, for a weird "pulsating" effect. If you beat him, you get the true ending.
Zerg Rush: Treasure rooms can become this if you don't hurry. You can also create them, intentionally or not, by forming long chains of enemies following you, then waiting for them to catch up.