Just a note, granting Vigilance after a creature has been declared an attacker will be giving it the ability after it's already been tapped to attack. So you may want a different ability or have the choice made at the beginning of combat step.

Yeah, granting vigilance to only attackers is actually really hard. Doing it at beginning of combat would work.

The phrasing is also going to be somewhat fiddly. It'd have to be something like "Whenever one or more creatures you control attacks or blocks, choose one - those creatures gain first strike UEOT; or those creatures gain +0/+2 UEOT."

The concept is a good one. Maybe: At the start of the combat phase choose one: First Strike or Vigilance. Creatures declared as attackers get the chosen ability until end of turn. At the start of the combat phase choose one: First Strike or +0/+2. Creatures declared as blockers gain the chosen ability until end of turn. It is very wordy but may work better with your concept???

I'll work on it some more. It was supposed to be like Glory of Warfare but a creature. That's turning out more difficult than expected. Thanks for the suggestions.

Gotta say, I like the trigger at beginning of combat, as opposed to the beginning of upkeep. You're less likely to forget it in combat, but rather likely to forget it during upkeep. I'm also not sure if you intended it, but drawing a blocking creature would change whether I wanted to give my creatures First Strike instead of the ability to block. That would cause a lot of frustration for the player of this card...

Changed it around a bit. In a two player duel it's simply one or the other. However if there are three players and both conditions are met, then you get both bonuses.