2020-04-17 : If an effect copies Swallow Whole, the copy will put a +1/+1 counter on the creature tapped to pay the additional cost of the original spell.

2020-04-17 : If the target creature is an illegal target by the time Swallow Whole tries to resolve, the spell won’t resolve. You won’t put a +1/+1 counter on any creature.

2020-04-17 : The target tapped creature will be exiled even if the creature you tapped leaves the battlefield or becomes untapped before Swallow Whole resolves.

2020-04-17 : You can tap any untapped creature you control, including a creature you haven’t controlled continuously since the beginning of your most recent turn, to pay the additional cost.

2020-04-17 : You must tap exactly one creature to cast Swallow Whole; you can’t cast it without tapping a creature, and you can’t tap additional creatures.