Acquired Mutation

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 the creature doesn’t meet any of the above exceptions and can attack, it must attack a player other than the controller of the spell or ability that goaded it if able. If the creature can’t attack any of those players but could otherwise attack, it must attack a planeswalker an opponent controls, a battle an opponent protects, or the player that goaded it.

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.