I think Ibb is the short one

Ibb & Obb is an adorable co-op puzzle-platformer with cute little characters who will be taunting you in your nightmares before you reach the end.

Its primary puzzle mechanic is a, uh... gravity line? Imagine that the ground is a mostly-horizontal line, and a character above it will be drawn downward, while a character below it will be drawn upward. Portals on the surface (or in walls) can be used to swap from one side of the line to the other, and you and your co-op partner will need to manage "who's on which side" to defeat enemies and overcome hurdles as you travel from left to right.

Gradually but surely, the game adds elements and complications which make for more brain-melting puzzles -- like character-specific portals (only one player can pass between them) and trampoline pads (jumping on them transfers your momentum to a character on the other side). Gravity management remains the core "thing" of the game, but additional foibles keep the overall design feeling fresh.

And then there are the twitchy, time-sensitive challenges, including: tandem-jumping over moving enemies, using gravity-inverting bubbles which can float out of your reach, and - what ultimately made my partner and I give up - using the other character as a platform while they're mid-jump.

Ibb & Obb does a great job of building up its puzzles' strategic complexity, and figuring those puzzles out was great motivation for most of the game's duration. Sitting and staring at the screen for minutes at a time, trading solution theories with your compatriot, is surprisingly satisfying.

The late game just cranked up its bar for precision platforming and reaction times too much, testing my appetite for masochism until it finally broke.

Good fun up until that point, though. Sincerely: this is the best co-op puzzler we've tackled in a while, despite its eventual, unreasonable difficulty.

Better than: Dyadic, Kalimba
Not as good as: Pitfall Planet
Unlike some other "relationship ruiner" games: here, you can commiserate against a shared enemy (the game).

Progress: Got part-way through level 13 of 15.