Just a quick question - how long does Spawn of the Sleeper last? From the card text it seems to be permanent. Is that correct? If it is permanent, as Spawn of the Sleeper is an event card how would your opponent retake control of their character or otherwise undo it once it takes effect?

Here's the card text:

[Madness]

Action : Choose a character that has gone insane as the result of a T struggle this phase. Take control of that character.

Thanks in advance for your help. I've got a new Cthulhu/Hastur deck I'm going to try out on some unspecting friends this Friday night, and I want to have all my inmates in a row rules-wise.

Here's the relevant section of the FAQ:

(v1.0) Duration of Effects
If a triggered effect has no specified
duration, then the effects of that
ability expire at the end of the current
phase. “Put into play,” “Remove from
play,” and “Take Control” effects are all
an exceptions to this rule, and unless
specified by a specific duration are
considered to be permanent effects.

So, control changes permanently, unless it changes again due to card effects or the character leaves play.

Ah, the good ol' FAQ, I should've known. Thank you for answering my question, that was a big help.