If I was going to use the illithid / mind flayer...

If I was going to use the mind flayer, keeping the stats as is (but calculating new figures like DCs, CMB and CMD), what would his new CR be? I'm assuming it would be lower, but I could be wrong.

I'm not sure (I haven't seen the actual Mind Flayer stats before) but you could always, after doing the conversion work, compare against the "Monster Stats by CR" table in the bestiary and see where about it falls.

While I do not recall where it is, there are rules for this in the books that indicate it would be -1 CR if a straight conversion of stats (quick & dirty). However, if you update the feats and everything else along with it, there shouldn't be a CR change.

@Johnico, thanks, the table is really helpful and I think the illithid looks like a CR4-5 creature.

@Da'ath, I might try to update the creature, but the problem is that I don't get some of the ideas presented, like 3/4 BAB and stuff (I mean, how do you do 3/4 of +0 or +1?).

Use total HD x 0.75 in a calculator, round down.=)

Wasn't there a fan conversion or two around?

@Da'ath, I might try to update the creature, but the problem is that I don't get some of the ideas presented, like 3/4 BAB and stuff (I mean, how do you do 3/4 of +0 or +1?).

It's the same BAB progression used for clerics, inquisitors, etc.

@Da'ath, thanks, I actually thought you were supposed to calculate BAB x 0.75 for every level :P

@Thanael, I tried googling it previously and didn't get anything satisfactory, checked again and I actually got some interesting stuff, mainly looking at: This and I want to get this but it requires me to register to download it so I'm going to put that off for a while. I actually also found another conversion, but it seems kind of weak, it was from a podcast or something. I may just use that first link I posted.

@Shadowborn, heheh, didn't know it was HD that was multiplied by the 0.75 :P

Registering at ENWorld is free, so I don't see why you need to put that off. o.O

Registering at ENWorld is free, so I don't see why you need to put that off. o.O

I'm not a fan of registering at forums, I've registered at a ton of them before just so I could get access to sometimes just a single file. I managed to find it on another site pretty easily, it doesn't seem that the guys who converted it (for some reason they renamed it 'thulid' (no, I don't think it's for legal purposes since they kept the same names for most, if not all, of the other conversions they did)) did a good job. He still has 8HD at CR7 and his AC and DCs haven't even increased, not that good to be honest. There was another conversion I saw, but it's to the effect of the forbidden lore book.

Yep the one on ENWorld is the one I remember. Sign up on the ENWorld forums, they're great!

Also i found this Monster Mash Bestiary pdf from a link to d20radio in this post

This is Chronicle's ongoing supplemental for the Monster Mash segment.

Soon it will be properly fleshed out with a more polished and complete presentation!

Episode 4 - Beholder and Oread
Episode 6 - Hook Horror and Ephemeral Swarm
Episode 7 - Cerebrilith and Mind Flayer
Episode 8 - Sylph, Shaedling and Banshrae
Episode 9 - Byakhee and Umber Hulk
Episode 10 - The Abishai + ToC
Episode 11 - Glastig and Warbound Impaler
Episode 12 - Boneleaf and Mi-Go
Episode 14 - War Troll and Tomb Spider