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Trample is a static ability that modifies the rules for assigning an attacking creature’s combat damage. The ability has no effect when a creature with trample is blocking or is dealing noncombat damage. (See rule 510, “Combat Damage Step.”)

The controller of an attacking creature with trample first assigns damage to the creature(s) blocking it. Once all those blocking creatures are assigned lethal damage, any excess damage is assigned as its controller chooses among those blocking creatures and the player, planeswalker, or battle the creature is attacking. When checking for assigned lethal damage, take into account damage already marked on the creature and damage from other creatures that’s being assigned during the same combat damage step, but not any abilities or effects that might change the amount of damage that’s actually dealt. The attacking creature’s controller need not assign lethal damage to all those blocking creatures but in that case can’t assign any damage to the player or planeswalker it’s attacking.

Trample over planeswalkers is a variant of trample that modifies the rules for assigning combat damage to planeswalkers. The controller of a creature with trample over planeswalkers assigns that creature’s combat damage as described in rule 702.19b, with one exception. If that creature is attacking a planeswalker, after lethal damage is assigned to all blocking creatures and damage at least equal to the loyalty of the planeswalker the creature is attacking is assigned to that planeswalker, further excess damage may be assigned as the attacking creature’s controller chooses among those blocking creatures, that planeswalker, and that planeswalker’s controller. When checking for assigned damage equal to a planeswalker’s loyalty, take into account damage from other creatures that’s being assigned during the same combat damage step, but not any abilities or effects that might change the amount of damage that’s actually dealt.

If an attacking creature with trample or trample over planeswalkers is blocked, but there are no creatures blocking it when damage is assigned, its damage is assigned to the defending player and/or planeswalker as though all blocking creatures have been assigned lethal damage.

If a creature with trample over planeswalkers is attacking a planeswalker and that planeswalker is removed from combat, the creature’s damage may be assigned to the defending player once all blocking creatures have been dealt lethal damage or, if there are no blocking creatures when damage is assigned, all its damage is assigned to the defending player. This is an exception to rule 506.4c, and it does not cause the creature to be attacking that player.

If a creature without trample over planeswalkers is attacking a planeswalker, none of its combat damage can be assigned to the defending player, even if that planeswalker has been removed from combat or the damage the attacking creature could assign is greater than the planeswalker’s loyalty.

Multiple instances of trample on the same creature are redundant. Multiple instances of trample over planeswalkers on the same creature are redundant.

For a player to mill a number of cards, that player puts that many cards from the top of their library into their graveyard.

A player can’t mill a number of cards greater than the number of cards in their library. If given the choice to do so, they can’t choose to take that action. If instructed to do so, they mill as many as possible. Similarly, the player can’t pay a cost that includes milling a number of cards greater than the number of cards in their library.

An effect that refers to a milled card can find that card in the zone it moved to from the library, as long as that zone is a public zone.

If an ability checks information about a single milled card but more than one card was milled, that ability refers to each of the milled cards. If that ability asks for any information about the milled card, such as a characteristic or mana value, it gets multiple answers. If these answers are used to determine the value of a variable, the sum of the answers is used. If that ability performs any actions on “the” card, it performs that action on each milled card. If that ability performs any actions on “a” card, the controller of the ability chooses which card is affected.