My suggestion is to let Slimes wear Armor. To be a bit more precise, I am suggesting that Slimes be given the ability to wear HELMETS.
This could be an option that is toggled on and off, and would read as "can wear armor=(0 or 1)".
It would be OFF by default, but would give the option to spawn in special slimes that HAVE helms on. This would open up a LOT of possibilities.
Slimes with Helmets. Meh. Boring?
Players being chased around by INVISIBLE SLIMES WEARING SKULLS!?! WHAT!?! AWESOME!
Or even Invisible Slimes disguised as a CHEST hiding in a temple... Just WAITING for the players to happen upon them.