Watchful Radstag

If a player has fewer cards remaining in their library than the number of rad counters they have when the triggered ability resolves, they’ll mill as many cards as they can.

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

Rad counters are a kind of counter that a player may have. They’re not associated with any specific permanents.

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.

Watchful Radstag “evolves” when its evolve ability resolves and a +1/+1 counter is put on it. If a replacement effect causes the evolve ability to put more than one +1/+1 counter on Watchful Radstag, its last ability triggers only once. If no +1/+1 counter is put on it (perhaps because it left the battlefield while its evolve ability was still on the stack), then its last ability doesn’t trigger.

The token copy won’t copy counters or damage marked on Watchful Radstag, nor will it copy other effects that have changed Watchful Radstag’s power, toughness, types, color, and so on. Normally, this means the token will simply be a Watchful Radstag, but if any copy effects have affected the original Watchful Radstag, the token will take those into account.