If I activate 2 Orb of Regrets against Stalwart Poro and then challenge the battlefield it's on, will the second Orb cancel out the shield effect?

Ruling: No, the second Orb of Regret will not cancel out the shield effect. The second Orb trigger will not reduce the Poro's might again since it's already at 1 might from the first Orb.

Sequence:

• Both Orb of Regret triggers resolve, reducing the Poro to 1 might (the second trigger has no additional effect)
• When you attack the 1 might Poro, the shield activates and increases it to 2 might