From the description of Udyr's Tiger Stance:
(Stance) – Activation: Udyr's next attack will deal his current attack
damage in addition to magic damage over 2 seconds.
If Udyr selects tiger stance, waits for the cooldown to refresh, attacks an opponent, then re-activates tiger stance and attacks again, what will happen? Is the magic damage dealt twice?
Best Answer
Been maining udyr for a couple of months (a source for the answer)
Basically, the buff is extended, not doubled. You still deal the same damage over 2 seconds, but the damage may be extended to 3 or 4 seconds depending on when you apply the buff. If you look closer, you see that udyrs bleed ticks for half the displayed damage every second for 2 seconds.
Assuming you deal 100 damage over 2 seconds, and strike your opponent again with the buff directly after the 1st tick:
Tl;Dr - you dont apply a 2nd stack of the bleed effect. You simply prolong the initial effect.