Atomix

this creature enters the Battlefield tapped

{t}{6} sacrifice give a -1-1 counter to all creatures and a Radioactive counter to all other players if a creature
would die put another -1-1 counter on all creatures and a Radioactive on all other players

if this creature deals damage to a player give them Radioactive counters equal to this creature power

Radioactive (if a player has 21 Radioactive counters they die)