Feral Ghoul

Rad counters don’t go away as steps, phases, or turns end. They only go away when an effect instructs a player to remove rad counters from themselves.

Any effects (such as proliferate) that interact with counters a player gets, has, or loses can interact with rad counters.

There is an inherent triggered ability associated with having rad counters. This triggered ability has no source and is controlled by the active player. The full text of this ability is “At the beginning of the precombat main phase of a player with rad counters, that player mills cards equal to the number of rad counters they have. For each nonland card milled this way, that player loses 1 life and removes one rad counter from themselves.”

Use Feral Ghoul’s power as it last existed on the battlefield to determine how many rad counters each opponent gets.

In a game using the shared team turns option, such as an Archenemy or Two-Headed Giant game, the inherent triggered ability associated with rad counters triggers once for each player on the active team that has rad counters. Each instance of that ability is controlled by one of those players.