When Bakersbane Duo enters, create a Food token (A Food is an artifact with ", , Sacrifice this artifact: You gain 3 life.").
Whenever you expend 4 (You expend 4 as you spend your fourth total mana to cast spells during a turn.), Bakersbane Duo gets +1/+1 until end of turn.
Vintage
, 
, Sacrifice this artifact: You gain 3 life.")