I actually think this would be a novel idea, since creepers are pretty much the mascot of minecraft.
On a side note, how about having Ghasts drop some item extremely rarely which allows you to make a "ghast mask" (if you don't get it, sound it out.) Which helps protect you from lava slightly. Nothing overpowered though.
I like using a creeper jack'o'lantern as my pumpkin texture.
There's a mod that adds paper masks on this page (you have to scroll down nearly half the page since anchors are broken right now.) I don't think they help hide you from mobs, but I suppose someone could ask for it.