Here is my current list. There are some interesting cards, so I’ll go over them.
4 Acro Bike/4 Roller Skates/4 Unown
It draws well without Shaymin-EX to help in the mirror.
2 Ultra Ball
There is no need to fetch Shaymin, is there?
It helps if/when you fall behind.
Overall, this list will probably beat the mirror, item lock if it goes first, and anything else if it can outspeed. As always, feel free to comment. Please note that this is an experiment.