Mana is kinda odd on defense, and I don’t really fully know if this 100% accurate but from what I’ve observed:
- After every turn, a defender gets 1 unit of mana
- When a tile hits them, they get half a unit of mana. This mana gain decreases slightly the higher your combo goes too… I’ve noticed that there’s some kind of soft cap to prevent a defender from charging from 0 to fully if they’re hit by a big combo, but I don’t have much data nor numbers to back up my observation.
However, I’ve noticed that the 0.5 tile breaks can make a difference for defense to help them charge a bit faster. So with that in mind costume bonus + level 17 troop should be enough as that gives you a 16% speed bump. Adding the 2% from emblems would just make it 18%, which isn’t enough to take your fast hero to 6.5 tiles (they reach that at 24% speed bonus, which you can’t do without mana buffs)
In summary, I’d say just pick crit if you’re ok giving your lvl 17 mana troop to that hero. Or pick mana if you’d rather give them a level 11 mana troop, and save the better one for another hero