And also, unlike most poisons, Habunake actually has decent Special Attack so it can actually USE Crunch and other special moves.
What about Toxic Fang, though? Yeah, it's a lot weaker than Sludge Bomb.. but it's got about the same chance of poisoning and instead of normal poison, it's Toxic-type poison.
I don't know about Rest and Shedding. I hope it does work that way, though. Too bad Habunake is the only one worth using who learns it (I think the only others are Dratini, Dragonair, Metapod, Kakuna, Sanakirasu, Karasarisu, and Mayorudo.. maybe Ekans/Arbok, I can't remember...)