My opponent had Jubilant Mascot on the battlefield. They also had Gisa, The Hellraiser. When they went to combat they had no mana available. The ability to pay 3W to Support 2 went onto the stack for Jubilant Mascot and they could not pay it. They still got to target my creatures with the Support 2 triggering Gisa. The card does NOT say, "Target two creatures then if you pay 3W..." The Support ability should have never gone onto the stack which meant that nothing should have been targeted and Gisa should not have triggered.