Failure to Return Priority after Opponent Action
During a Brawl game, my opponent had eight nonland permanents in play, one of which was Bolas' Citadel, and I had (amongst other things) 4 energy, and a Dynavolt Tower in play. In my opponent's end step, they passed priority and I cast Explosion, X=5 targeting them with the damage and myself with the card draw.
My spell put a trigger on the stack from Dynavolt Tower to gain 2 energy. After this trigger resolved but before the spell resolved, my opponent flashed in (Alchemy modified) Orcish Bowmasters which I allowed to resolve, bringing them to nine nonland permanents. In this window, I had 6 energy. more than the 5 needed to tap the untapped Dynavolt Tower to deal 3 damage to any target. Tapping the Dynavolt Tower to deal 3 damage to the Orcish Bowmasters would have allowed me to kill it before Explosion resolved, meaning Orcish Bowmasters' triggered ability to deal 1 damage to me and Amass Orcs 1 for my opponent for each of the 5 cards Explosion would draw would not resolve.
Under the rules of Magic, between Orcish Bowmasters resolving and the next spell or ability on the stack (Explosion) resolving, my opponent and then I should consecutively have received priority before Explosion resolved. My opponent's priority in this case was automatically passed because they had no available spells or abilities (I assume - they had little or no available mana and no on-board abilities they could activate) but mine should not have been, as I had sufficient energy to activate my untapped Dynavolt Tower, and multiple legal targets for its ability. I had no realistic basis to anticipate my opponent's play so it is not reasonable for me to have set a pre-emptive stop in this case.
In this case, I did not receive priority - to be honest I don't remember whether I received it (when I should have) when the Orcish Bowmasters were on the stack, but I definitely didn't receive it after they resolved but before Explosion resolved. Because I didn't receive priority there I was unable to tap Dynavolt Tower and pay 5 energy to deal 3 damage, removing the Orcish Bowmasters. As a result, when Explosion resolved and I drew 5 cards, it triggered the ability of Orcish Bowmasters 5 times, dealing 5 damage to me and creating a 5/5 Orc Army under my opponent's control. This Orc Army represented their tenth nonland permanent allowing them to activate the ability of Bolas' Citadel to sacrifice ten nonland permanents and deal ten damage to me, reducing my life total below zero - where had I received priority to take the desired game action at the appropriate point, they would never have had more than nine nonland permanents at any juncture.