This spell can't be countered.
Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Thrun, Breaker of Silence can't be the target of nongreen spells your opponents control or abilities from nongreen sources your opponents control.
As long as it's your turn, Thrun has indestructible (Effects that say "destroy" don't destroy that permanent. An indestructible creature can't be destroyed by damage.).
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