Ji, Golgari Plague Bearer

Apprentice (You may have two commanders if one is
an Apprentice. If it's not an apprentice, ignore the text
in braces.)
At the beginning of your end step, target
opponent gains a poison counter. {Then, place
a -1/-1 counter on target creature you control.}
"I'm still working on how to poison my opponents
while allowing my friends to stay clean."