The Exigency Ward

At the beginning of each upkeep,
put a terminal counter on target creature
if their controller attacked or targeted another
player or permanent they did not control last
turn.
Creatures with terminal counters gain a
-1/-1 counter and tap at the end of each
turn or two of those counters if they
attacked since the last end step.
"Best course of action? Quarantine...Separately".