If you have a card in hand at the moment the trigger condition occurs, Bloodhall Priest’s ability won’t trigger, even if you can get that card out of your hand immediately afterward. If you have a card in hand as the ability resolves, it has no effect. No damage will be dealt.
Bloodhall Priest
If you discard a card with madness while a spell or ability is resolving, it moves immediately to exile. Continue resolving that spell or ability, noting that the card you discarded is not in your graveyard at this time. Its madness triggered ability will be placed onto the stack once that spell or ability has completely resolved.
Casting a spell with madness ignores the timing rules based on the card's card type. For example, you can cast a sorcery with madness if you discard it during an opponent's turn.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Mark Winters
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