This makes them a powerful tool for dealing with tough creatures your opponents may control
You can use it on your opponent's turn and release it on your turn to strengthen it, but since strengthening is treated as an activation effect, it can only be used during the main phase
This is a hard once per turn effect, meaning if you have another Caligo Claw Crow in your hand, you cant activate both of them

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* You could maaaaybe lower retreat to 1, but Id say thats in exchange for lowering HP a little bit more, down to 80