Personally i would have to say Yveltal because when it comes to its
story when it dies it drains the life force of other pokemon so we
could put Mewtwo in there and if for some reason Yveltal decides to
turn into a cocoon again it will kill mewtwo and everyone else but
a good competition would be Giratina due to being literally stuck
in the distortion world and would probably just take it to the
distortion world to save everyone's life but in game Yveltal is a
dark type and Giratina is a Ghost type soo...
I like Mew, but I'm kinda biased based on my preferences. I think
some people would like Arceus, but I feel like Arceus is that
kinda-spoiled kid who only knows how to do the super OP attacks but
has really low stamina, health, and everything else. IDK, that's
just what I think
I'm thinking Arceus or the regi trio. Arceus is really strong and
has good stats, but the regi trio pokemon are very strong as well.
Also, the regi trio pokemon are easier to get lol.