Nicely done!
At first I assumed the double jump you get from carrying a slime was the only way to get to higher places, but it seems the extra mass gained perfectly offsets the player's natural jump height. So carrying the extra slimes are more useful for defeating enemies, something I was hesitant to do originally since that lost the slime permanently.
I also like how the slimes can be placed down on pressure plates to activate levers, another reason to weigh yourself down with them. Though I found if I wasn't very careful they could slip off the pressure plates unexpectedly.
The difficulty ramps up nicely, as does the level length until the final stage, which was possibly as long as all the others combined. :D