Open a random number generator on google. Set it to 1-1025, roll it, and the number you get is the pokemon you will use to battle the person above you.

I got Jumpluff. Now roll to see if you can beat me.

SAMPLE:

U1: #0100 - Voltorb. (Explanation on how they would either win or lose against the pokemon above)
U2: #0250 - Ho-Oh. (Explanation on how they would either win or lose against Voltorb)