Hey everyone, so I'm confused about the instant card Take into Custody. Since this is an instant and not an enchantment, how long does this card stay on the battlefield/how long is the target creature tapped? Is it only for one turn and if so, when is a good time to play this card to "get the most bang for your buck"?
It doesn't "stay on the battlefield," since its an instant. What it does is tap a creature, and then, when the creature's controller's next untap step rolls around, the creature will stay tapped. It will untap as normal on the following turn. Any time a card says "next" it only checks once, so you don't have to worry about a given spell or ability after the step/phase mentioned passes.
Take into Custody is an instant spell, so it goes to the graveyard as the last step of its resolution (C.R. 608.2k). The creature won't untap "during its controller's next untap step" (C.R. 611.2c; see also C.R. 611.2a). The spell's effect won't keep the creature from untapping at any other time (including during other untap steps).
Cheers
EDIT (Apr. 25, May 11): Clarification.
EDIT (Dec. 21): Add rule citation.