Bubblins made of different liquids should have different effects/behaviors, perhaps lava bubblins are somewhat more keen to fight, while acid bubblins damage attacking mobs, but don't attack back. Oil bubblins could slow the enemy.
Aww! I love the spriting as well as the variety. They kind of remind me of the virorbs except a lower-leveled form. I am guessing thats what these could be. They would be placed on the lower leveled planets and stuff and possibly some of the prettier, less ugly planets (ugly planets being such as the lava-like planets and the such)! ^.^ So cute!
I was wondering though, since oil and lava are much more viscous than water, would that give them some extra strength? Like is there any ways that you could make a bubblin not pop after a single hit?