I think it's mostly that titan magic just negates his race's magic, so that's probably why was able to trap king in that nightmare.

@BoxmanCool

Ah

My headcanon was Collector magic can KILL Titans still but can't affect them in any way (meaning that Collector magic can only hsrm or kill them but cant transform or affect them in any othwr way) Plus I thought the whole "my powers don't work on King" meant that Collector magic can only hurt and kill them but do nothing else lol

So MAAAAAAAAYBE the only real canonical reason this happened that would work with my headcanon/what The Collector himself said is that King is still young so he isn't as immune to it yet (hence why despite the Titan magic thing he was still trapped in that nightmare)

Not bad