
TrampleTrampleExcess combat damage it deals to a blocker carries over to the player or planeswalker it's attacking.
When Old-Growth Troll diesdiesA creature dies when it goes from the battlefield to a graveyard. Being exiled or returned to hand is not dying., if it was a creature, return it to the battlefield. It's an Aura enchantment with enchant Forest you control and "Enchanted Forest has ': Add
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,
, Sacrifice this land: Create a tapped 4/4 green Troll Warrior creature token with trampletrampleExcess combat damage it deals to a blocker carries over to the player or planeswalker it's attacking..'"
Hover an underlined rule to see what it means.
Read from the rules text. A card that enables a keyword makes or is the thing; a card that rewards it gets better when you have it. Two cards interact when one enables what the other rewards.