Solar Vs Worlds Funnest Mxy

Who wins?

Mxy wins.

In the end, they essentially destroyed the same thing (a multiverse++.) However, Mxy demonstrated the ability to recreate that which he destroyed, with a literal snap--something Solar was not able to do on such a vast scale.

When did Mxy destroy the multiverse?

During World's Funnest.

...And he destroyed more than a multiverse, btw. Quite a bit more, in fact.