Yeah, I only meant, that leaving Marco on Earth was the thing he couldn't predict. And neither he could know about the scissors (and the shit Marco had to through to achieve them)
Maybe he thought Star would take Marco with her so he can either:
- use him as a weak chain and capture him again
- capture Marco's family thus destabilising the party (if Marco wants to save them but Butterflies refuse to help) or making them act the way he needs (going to save parents and of course getting into a trap)
But now this point of the situation is not very predictable for Toffee as Marco is left behind without (what it seems like) any possible connections with Star. His parents are at least a bit protected by Marco (plus, surprise, he definetely got better in combat, probably has some skills from his 16 years journey). Etc.
I'm not sayng it's impossible, but in general: a possible fighting back from potential hostages, those hostages possibly don't have any value now, informing Star about capturing Marco could be pain in the ass and again - potentially useless, some probably undiscovered surprises for Toffee (like Scissors or some Marco new skills)... See, too much "probably" and "possibly" for Toffee.
And again - taking Marco to Mewni is also not a solution. If he's safe, Toffee can catch his parents. If they are safe - then friends or other relatives, etc. In that case Toffee would always have a target. But current situation brings him enough uncertainty to at least temporary slow him down and fuck up his plans