Good concept and artwork. Movement feels really viscous and the spark mechanic works a bit buggy (i cant recall it sometimes). Platformer movement issues are a common thing in unity try chaning sensitivity and snap values for Horizontal axis in Input Axis settings or just check for pressed keys directly. For jumping I suggest this video. Also you can take a look at a game featuring similar mechanic. Good luck :)
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Thanks for the reply! About the bug with the spark, if the spark gets taken by a monster, it will not return to the player. You will need to go there and pick it up manually (if this is what happened in your case) :) . Platforms were added the last second, so there was not much time to optimize them . Huge thanks for the two url's they are a great help!