"According to Liber Mutatis(page 20)

A marked character (of Tzeentch)...He can acquire and cast spells with the Tzeentch trait.... Powering his spells like a Wizard.

So I assume that means channeling power. However, none of the spells I have seen, list any Power Requirements...

Thoughts?"

How should my player do this?

jh

The Chaos Sorcerer entry on page 26 says "They favour spells with the Tzeentch or Chaos traits and do not need to channel or spend power to fuel their spells."

The first sentence of the sidebar you're quoting from on page 20 of Liber Mutatis says:

"Assigning a Chaos Mark to an NPC is a new option GMs can use to distinguish or tailor encounters to suit the story or challenge his players."

From there it goes on about NPCs. It's really an NPC power, and not exactly meant to be used for PCs.

Clearly you're free to do whatever you want with your game. Not trying to stop you. I'm just saying it's like if a PC wanted to buy an NPC action that was triggered by A/C/E spends. There's not a clear PC-equivalent to use, and you're gonna have to do some converting or work-around. Speaking of which, many of those Tzeentch spells will also have A/C/E references on them, so you'll have to figure out how you're going to convert or work around them.

Personally, I'd probably just hand the PC the Witch Career and the Hedge Magic talent and/or Dark Magic order talent. Those are the closest PC equivalents. Until you find time and energy to figure out any Tzeentch spells you want to convert, just give them access to the Dark Magic spells (Black Breath of Death, Black Nimbus of Arnizipal, Doombolt, Dread Malaise, Sadistic Glee, Soul Drain) as those actions use the familiar PC mechanics and don't need converting at all.