wait what if your opponent has four creatures otb when you do the Mirrorweave + Biovisionary ?

Biovisionary says at the beginning of "THE" end step not "YOUR" end step...so a tie?

I believe your biovisionaries take priority and the ability enters the stack first, with the opponent's coming second. That means that theirs will resolve first, and they win.

It's a little slower than your other spells, but you might want to throw in an Infinite Reflection or two, because it doesn't do the Mirrorweave thing and let your opponents win.

And, just to be clear, if you and your opponents both have 4 creatures and you Mirrorweave Biovisionary , in a two-player game, the player who's turn it is loses.

I did have Infinite Reflection in there before, but I found myself rarely using it because I usually have a lot of tokens and not too many creatures. But then again, I didn't know about the Mirrorweave priority problem in the past, so perhaps I should return one in just to be safe. Maybe if i switch the deck to use creature clones instead of token clones it will become more useful. Thanks!

It's not that there's any reason not to run Mirrorweave , you just have to remember not to cast it on your turn. It's an instant, though, so it's fine.