Any character action that requires you to exert a card needs dry ink - meaning that card has been on the board since the start of that turn
However, WotC is looking out for Urza's Saga
The only way for the Nighthawk to kill the Skyfisher is if Sara blocks Nicks Nighthawk with it, or if Sara attacks with the Skyfisher and Nick blocks with the Nighthawk
Argentum Armor offers a massive buff and can obliterate opposing permanents, and if you put Helm of the Host on Sokka and Suki, things can get even more out of hand more quickly since youll start getting even more Allies and even more Equip triggers
Its unfortunate that she is not a Human, but we are welcoming of all races here
Note that cards with scry or other similar effects will strengthen the Courser, and this is another tool to empower an already-powerful multiplayer deck type