I read through When does marking occur?, but I'm still not sure that the sequence of events actually happens the way I'm hoping it happens for the following combo to work.
I'm a level 16 heavy blade polearm fighter with a Glaive, and I've got the usual feats like polearm gamble, polearm momentum, etc.
I'm looking at the feat Tactical Superiority which says:
Whenever you hit an enemy marked by you with an OA, that enemy is slowed until the end of your next turn.
I'm not sure when the mark applies during the following attack sequence: Say I'm standing in a square, and an enemy enters a square adjacent to me, triggering my Polearm Gamble, so I attack it with an OA. Could I mark him as I'm attacking, triggering the Tactical Superiority feat, slowing him until the end of my next turn? Or does the creature have to be already marked by me before entering my adjacent square?
In short, a mark says it can be applied whenever you attack, whether you hit or miss, but can you mark as part of the attack?