Your opponent can choose to add one card to their hand for each mulligan you take
Krenko, Mob Boss and Goreclaw, Terror of Qal Sisma are the two easiest to pilot both are single-color, both cost about $2, and both have a one-sentence game plan
Boromir, Warden of the Tower This three-drop 3/3 is our first mono-White card and last card before the Top Five proper
Clearly, Im not an advocate of not allowing them to do anything at all, but thats towards the other end of the spectrum
Id favor unblockable effects and haste enablers over fight and bite spells, since haste and unblockable enablers are useful even when your win conditions arent around, but bite spells are less effective when youve mostly got tokens (deathtouch notwithstanding)