Dogs are indeed white. Affa Guard Hound etc. Creature type Hound is traditional.

"~ gets +1/+1 for each other attacking creature"? "~ gets +1/+1 if another creature is attacking?"

Yeah, something like that. Not totally settled, and whichever I choose, I probably want it to be a mechanic used on some other cards too.

I also want it to be fairly vanilla, in this slot.

Right - now THAT is a dwarfish mechanic. The more dwarves back at home manning the pumps, the stronger the guards are. May keyword it.

The mechanic was slightly fiddly to keep track of, but kinda fun and introduced some tension as you try to keep enough creatures back to keep a withered creature alive; or keep creatures safe from soul drain or similar.

Yeah, it worked fairly well. It's defensive, certainly, but the deathtouch and evasion helped counteract that and let games actually end. (Don't remove Scary Mask entirely unless you add some more common evasion.)