If I have 2 Arbor Knight in play, during challenges phase, could I pay 6 gold to +6 STR?

Or only could pay 3 add +3 str even I have more than 1 Arbor Knight?

Tks a lot.

RRG, 12:

Limits and Maxima

“Limit X per [period]” is a limit that appears on cards that remain in play through the resolution of an ability’s effect. Each copy of an ability with such a limit may be used X times during the designated period. If a card leaves play and re-enters play during the same period, the card is considered to be bringing a new copy of the ability to the game.

Oh thanks.

So powerful card.