Daemons vs daemons?

The game I got on Thursday is going to be against Khorne daemonkin. I know he uses a Thirster and the lord of skulls! I don't currently have 1850 points of slaanesh but I asked if I could use the forgeworld rules and he said yes after some convincing ;) 

The stats are gargantuan creature ws10 bs3 s7 t7 w6 i10 a5 ld10 sv -3++ 

It's sword has instant death and for every wound I roll a d6. For every 2+ she gains a wound up to 10. And all units needs to pass a Ld test to attack. So she is pretty decent for 666pts :) what I'm worried about is the Lord of skulls. Not sure how to kill it. I might just need to tie it up with some daemonettes or something. I might roll armor bane on the prince or something. Either way it is going to be an epic battle! I'm just hoping it will be done until that. I also need to paint a daemon prince but if I don't have time for it I will probably use My Belakor model as a slaanesh prince :)

I also asked a friend to paint the 4 citadel woods we got for the club since I don't want to spend my limited time painting trees when there are daemons that needs my attention. He won't do it for free though but with all the paints I would've needed to buy I got away cheap.