Ice Cream Sand Witch

yeah but inflicts damage equal to the health  Pyukumuku had before it faints. So it has to have health equal or higher then garchomps? So I have to use pain split? Or am I missing something?

Hmm. What is the average level that someone's Pokemon is by the time they face Garchomp? like, 35-40? because a 0 IV, non-invested Garchomp at level 75 has almost twice the HP of a 31 IV, 252 HP EV Pyukumuku at level 40. 

So in summary, two, maybe three Pyukumukus can pull it off. Pretty similar deal with Arceus, although 2 Pyukumukus have a higher chance of pulling that one off. 

Level cap at that point is 45 (though someone could ignore the cap and keep leveling), and Dittoceus level cap is 60.