Can I sacrifice it once its ability is on the stack so that I still get the mana but my opponent does not gain control of it?
I would like to preemptively point out that Witch Engine's ability is NOT a mana ability:
Because the ability is targeted, it is not a mana ability. It can only be activated when you have priority, and goes on the stack like other non-mana abilities.
I ask because some cards have abilities that are countered if the permanent that produces the effect is no longer on the battlefield when the ability resolves (e.g. the exchange part of Gilded Drake), and this card seems weird enough that it might have an interaction like that. In other words, does an opponent have to actually gain control of Witch Engine for the ability to resolve, or will the mana-producing part of the ability resolve even if Witch Engine is no longer on the battlefield to allow the control-changing part of the ability to resolve?
Can I sacrifice it once its ability is on the stack so that I still get the mana but my opponent does not gain control of it?
I would like to preemptively point out that Witch Engine's ability is NOT a mana ability:
I ask because some cards have abilities that are countered if the permanent that produces the effect is no longer on the battlefield when the ability resolves (e.g. the exchange part of Gilded Drake), and this card seems weird enough that it might have an interaction like that. In other words, does an opponent have to actually gain control of Witch Engine for the ability to resolve, or will the mana-producing part of the ability resolve even if Witch Engine is no longer on the battlefield to allow the control-changing part of the ability to resolve?