It's my turn and there's an empty battlefield "Sunken Temple". I decided to conquer it, so I move my Noxus Hopeful to it. In my priority, I play a Blood Rush without repeat. I conquer the battlefield, so the question is: can I pay 1 to draw a card by conquering Sunken Temple with a Mighty unit?
No, you cannot use the effect of Sunken Temple to draw a card in this scenario.
Reasoning
According to RiftJudge FAQ #4146 and #8999, Sunken Temple’s ability is a triggered ability that requires the unit conquering the battlefield to be Mighty (having 5 or more Might) at the exact moment the conquer occurs.
- Noxus Hopeful's Might: Noxus Hopeful has a base Might of 4.
- Blood Rush Effect: Blood Rush grants the target a Might bonus specifically "while it's an attacker."
- Timing and Status: When you move your unit to an empty battlefield to conquer it, your unit is not an attacker; it is simply a unit moving to an empty battlefield. Because your unit is not currently attacking, the Might bonus from Blood Rush is not active, and its Might remains 4.
- Failure to Trigger: Because your unit’s Might is only 4 at the moment the conquer is established, the "Mighty" condition on Sunken Temple is not met. Consequently, the ability does not trigger, and you cannot pay the cost to draw a card.
Even if you were to order your actions differently, Sunken Temple checks for the "Mighty" status at the precise moment of the conquer. If the unit is not Mighty at that exact time, the ability fails to trigger entirely, and buffs applied later or from conditional states that are not met do not retroactively satisfy the requirement.
Note: I could not fully verify this ruling against the retrieved rules, as the specific interaction between Blood Rush and the Assault keyword was not explicitly confirmed in the provided documentation.