Creeper Mods?

MCreator is insanely cryptic in many ways but nonetheless... I would like to make a mod that tries to mimic Elemental Creepers or something similar, basically I would like to add some custom Creepers in a custom dimension and whatnot. But basically what I would like to do for starters is:

-How can I make one of my addon mobs create a block as he walks? If you remember, in Elemental Creepers the Magma Creeper creaters fire as he walks and I would like to replicate that.

-I would like to make a Creeper mob I've made create a structure upon exploding or something akin to that. Additionally, I would like to make a Creeper that creates a loot table upon explosion (like the Cookie Creeper creates a bunch of cookies you can collect when he explodes) or an entity (so for example when he explodes it spawns another mob in his place). 

Any suggestions?