When you see The Beamtown Bullies you immediately see the awful evil things you can do with them. I guess it would be easy enough to just jam some good ETB creatures (similar to the precon) to help opposition players but what are the best gifts that will help everyone at the table if I were to give it to an opponent?
Pioneer:UR Pheonix
Modern:U Mono U Tron
EDH
GB Glissa, the traitor: Army of Cans
UW Dragonlord Ojutai: Dragonlord NOjutai
UWGDerevi, Empyrial Tactician "you cannot fight the storm"
R Zirilan of the claw. The solution to every problem is dragons
UB Etrata, the Silencer Cloning assassination
Peasant cube: Cards I own
There are a few more cards that help all but one player such as hired giant boldwyn Heavyweights, hunted wumpus, and tempting wurm
druid of purification may also count as it lets everyone vote on what happens.