Watchful Radstag

Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)
Whenever Watchful Radstag evolves, create a token that's a copy of it.

Don't mistake timidness for defenselessness.

Fallout

Evolve (Whenever a creature enters the battlefield under your control, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)
Whenever Watchful Radstag evolves, create a token that's a copy of it.

Evolve
Whenever Watchful Radstag evolves, create a token that's a copy of it.

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

If Watchful Radstag leaves the battlefield before its last ability resolves, the token will still enter the battlefield as a copy of Watchful Radstag, using Watchful Radstag’s copiable values from when it was last on the battlefield.

If a creature enters the battlefield with +1/+1 counters on it, consider those counters when determining if evolve will trigger. For example, a 1/1 creature that enters the battlefield with two +1/+1 counters on it will cause the evolve ability of a 2/2 creature to trigger.

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.

If evolve triggers, the stat comparison will happen again when the ability tries to resolve. If neither stat of the new creature is greater, the ability will do nothing. If the creature that entered the battlefield leaves the battlefield before evolve tries to resolve, use its last known power and toughness to compare the stats.

If multiple creatures enter the battlefield at the same time, evolve may trigger multiple times, although the stat comparison will take place each time one of those abilities tries to resolve. For example, if you control a 2/2 creature with evolve and two 3/3 creatures enter the battlefield, evolve will trigger twice. The first ability will resolve and put a +1/+1 counter on the creature with evolve. When the second ability tries to resolve, neither the power nor the toughness of the new creature is greater than that of the creature with evolve, so that ability does nothing.

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.

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.

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

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.

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 token copy will have Watchful Radstag’s abilities. It will also be able to create copies of itself.

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.

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.”

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.

Watchful Radstag’s last ability won’t trigger if a +1/+1 counter is put on it for any reason other than its evolve ability resolving.

When comparing the stats as the evolve ability resolves, it’s possible that the stat that’s greater changes from power to toughness or vice versa. If this happens, the ability will still resolve and you’ll put a +1/+1 counter on the creature with evolve. For example, if you control a 2/2 creature with evolve and a 1/3 creature enters the battlefield under your control, its toughness is greater, so evolve will trigger. In response, the 1/3 creature gets +2/-2. When the evolve trigger tries to resolve, its power is greater. You’ll put a +1/+1 counter on the creature with evolve.

When comparing the stats of the two creatures for evolve, you always compare power to power and toughness to toughness.

Whenever a creature enters the battlefield under your control, check its power and toughness against the power and toughness of the creature with evolve. If neither stat of the new creature is greater, evolve won’t trigger at all.