剣士ガフガリオン
「いいか、一人残らず殺るぞッ！
生きて奴らを帰すなッ！騎士アグリアス
「何を言うか！
奴らを殺す必要はないッ！
「ここで奴らを殺してしまっては
まさにゴルターナ公の思うつぼ！
追い返すだけでいいッ！剣士ガフガリオン
「そんな器用なマネができるもンかッ！
It's from the game "Final Fantasy Tactics".
I don't really understand the last sentence.
My translation: "Like I can act that skillfully!"
Does 器用な真似 mean "act skillfully" or it means "skillfully pretend"?
For もんか, please see this answer. In a lot of cases, もんか expresses a strong sense of disbelief, denial, conviction, or challenge to another person.
This マネ/真似 doesn't mean copying, pretending, or imitation. It means behavior or act. Per デジタル大辞泉（小学館）:
行動。ふるまい。「ばかな真似はよせ」
Here 器用な真似 means something that requires skills or high level of ability to accomplish. In this context
そんな器用なマネができるもンかッ！
means "Something difficult like that is beyond my reach!"
