My opponent has 3 mountains and a Dragonspeaker Shaman in play (RR1 Dragons cost you 2 less to play)
I steal it off him with the 2/2 blue flying (You gain control of target creature and keep control until the 2/2 leaves play)
My opponent has only 3 land in play and despite not controlling the Shaman anymore still manages to cast a 4/4 Voracious Dragon the following turn.
In my next turn I "Repulse" the dragon. (Putting it back in his hand)
He then casts it again paying only 3 mana (instead of 5)