Rad counters are counters placed on players. At the beginning of your precombat main phase, you mill cards equal to your rad counters, then lose 1 life and remove a rad counter for each nonland card milled this way.
The Wise Mothman turns all that milling into +1/+1 counters, while cards such as Radstorm can proliferate radiation already spread around the table. Rad decks can even irradiate themselves when a stocked graveyard is worth the damage.
