Everyone uses jumpy, and it's the most trollish commander.
Then you can do others for further tourneys.
Oh, if many people sign up you can also do some FFA rounds :)
Or, in fact, since a trollnament doesn't have to be srs and standard, you could intermix modes as you please.
For example:
First round: 2v2
Second round: winners of 2v2's duel each other
Semifinals: survivors do FFA to ensure one finalist
Losers bracket: FFA to ensure another finalist
Finals: Grand duel between winner of winners bracket and losers bracket.