Struggle for Project Purity

The cards are milled all at once, which means abilities that trigger “whenever one or more nonland cards are milled” will trigger exactly once as long as at least one nonland card was milled.

The number of rad counters the attacking player gets when the “Enclave” triggered ability resolves is based on the number of creatures they declared as attackers. Removing creatures from combat won’t reduce the number of rad counters they get. Similarly, creatures that enter the battlefield attacking but weren’t declared as attackers won’t increase the number of rad counters they get.

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

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.

If you somehow control Struggle for Project Purity and no choice was made for it (perhaps because another permanent on the battlefield became a copy of it), it has neither of the two triggered abilities.

Keep track of how many rad counters each player has. Potential ways to track this include writing them down on paper or using dice, but any method that is clear and mutually agreeable is fine.