Actually, I think they look a lot like a slender bulette with Iron scales and longer limbs. Well, proportionnaly longer since they are just large, not huge. But there is some flesh showing between the plates that justify the possibility sneak attacks working on these beasties.
Let's analyze them thoroughly, shall we? (
geez, just one line of british impersonation and I'm annoying myself already!)
Strenghts
A strong AC of 30 (-1 size, +5 Dex, +16 natural). The warrior types will still hit most of the time with their first attack, but everyone else will be strugling.
They are also very annoying to rogues because they have blindsight 30 feet. That makes it very difficult to gain ranged sneak attack against them. Unless they are stunned, I see no other options. Especially since...
...their magic sense allow them to detect any magic items within 120 feet! Gaining surprise on these beasties is very tough even without accounting for their +18 spot skill. You probably can't count on them being flatfooted.
Roar: that is a very good opening attack. Every 1D4 round the steel predator can roar, causing 12D6 of damage and deafness for 2D6 round in a 30 feet cone. Fortitude 20 for half + negating deafness. Yes, it is a fortitude check, not reflex. Rogues will really hate them!
Improved grab: Usually, you face more than one steel predator at a time. As such I would strongly warn the wizard to avoid letting a steel predator near him at all cost. He's sure to grab and rake and make your life miserable if that were to happen. The fighter won't be too worried tough. The steel predator probably won't win a grapple check against him.
Initiative: +9 Heh, you know what that means.
DR 20/+4. One or two PC will probably be caught off guard by this on their first encounter. Of course, not if they are reading this
Speed: 50. This gives them a lot of tactical capabilities. Unless you stick close together they'll be able to pick on any isolated member. And if you stick together they'll be able to catch you all in their roar attack.
And of course: the dreaded
sundering bite!. Yes, it can be very annoying. It's certainly its most dangerous ability. +4 to sunder check and double bite damage (meaning 4D6+14) is very likely to cause a lot of trouble.
So So
Attack and damage. +19 and +17 X 2 is nit bad but it's not great either at that level. The PC have seen worse. Heck, the PC fighter
is "worse". Tordek at level 15 is supposed to do be +27!
Damage are also underwhelming. 2D6+7 on the bite will not terrify PC of that level. And the claws are only 2D4+3.
HP: 102 is OK.
Weaknesses :
NO MAGIC RESISTANCE. For a denizen of Acheron it is unusual but it means your wizard will have a field day. Their save are good though, but not unbeatable. And plenty of spell offer no saves.
They are also immune to sonic and electricity while they have 20 resistance to cold and fire. I guess I should have mentionned that in strenght but I'm sure you have noticed the one energy attack to which they are vulnerable: acid.
Oh yeah, and it has no reach.