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to beat; to attack (an enemy); to do away with; to finish off
チームで協力して敵をやっ付けた。
We cooperated as a team and defeated the enemy.
ゲームの最終ボスをやっ付けてクリアした。
I beat the final boss in the game and cleared it.
強い相手でもみんなでやっ付けられる。
Even strong opponents can be beaten by everyone together.