Shroomisaur
Smogon's fantastical fun-guy.
That's not entirely true, since its mixed/special sets are Aegislash's best sets at the moment. The real question is whether the huge Special Defense boost is worth losing the attack power boost of Spooky Plate or Life Orb. It's certainly a good option to consider!Except that Aegislash relies on boosting moves like swords dance and automize, as well as the ability to switch between forms with king's shield, all of which can't be used with AV
The Snorlax discussion thread has some excellent calcs demonstrating just how amazing Assault Vest Lax is at absorbing special hits, taking under 10% from a 252+ Volcarona Fire Blast, for example. Since Snorlax doesn't depend on status moves nearly as much as most walls, he makes for one of the best AV users.