Viper

+1: Create a 0/1 colorless construct artifact creature token named Snake Bite with "When this creature dies, put a -1/-1 counter on target creature"
-2: Until your next turn, creatures attacking you or planeswalkers you control get -2/-2 and lose first strike and double strike.
-6: You get an emblem with "attacking creatures opponents control get -2/-2. Constructs you control get +1/+0 and infect."