Oh man! As someone who similarly made a game around pocket dimensions I am glad you stuck with a creative interpretation of the theme. You have created a really neat and original mechanic for the platformer/-vania genre. The three-part projectile that sucks things into the dimensional hole or pushes things into it works very well. Because they only form when projectiles collide, there's this chaotic, unpredictable energy to the game's combat which is a lot of fun. Much better than just clicking a few times to kill an enemy. Very satisfying. The game's got a lovely pixel presentation that works well.
For constructive feedback, the imprecision of the projectile is kind of the point, but it can make direct targeting tricky. You sort of at times just have to trust the dimensions will find the right path to the enemy. Makes it quite satisfyingly challenging! I think it would be insanely easy to expand on this idea and urge you to - the concept is that distinctive. Plenty of elements you could add to with the dimension mechanic. Portal style puzzle mechanics would be a super nice complement to the action.
Great work! I enjoyed this a bunch and really liked the idea for the game. Please keep at it!