Advancing a non-standard Paladin mount

[Murrdox]

Okay, so here's the lowdown.

I'm creating a BBEG for my campaign.

10 Pal / 5 Blackguard

He has a Nightmare for a mount.

The question is... should I advance the mount as a Paladin's mount is advanced, or just use the standard Nightmare? Should I advance it just ONE increment, similar to how a Druid advances a more powerful animal companion? Any ideas? Thoughts?

In the end, I'll do what feels right to challenge my players, but I'd like to keep it in scope of the rules.

 

[FireLance]

Technically, a Pal10/Blk5 gets an undead companion and a fiendish servant, which could be a fiendish bat, cat, dire rat, horse, pony, raven, or toad. These gain HD and abilities according to his character level.

By the core rules, he may obtain the services of a nightmare as a mount by attracting one with the Leadership feat. The nightmare's advancement would be governed by the rules for that feat, so it would not gain the special abilities of a blackguard's fiendish servant. A 6HD nightmare is the equivalent of a 10th-level character, so your blackguard could potentially be served by a 9HD nightmare (the equivalent of a 13th-level character).

Alternatively, the nightmare could be a separate creature in its own right, so its abilities would not be tied to the blackguard at all. Remember to award additional XP for defeating the nightmare since the blackguard did not obtain its services as a class ability or the expenditure of a feat.

There is another feat in Dungeon #100 that allowed a blackguard to obtain the services of a nightmare in place of his fiendish servant. Offhand, I cannot recall the details, but my sense is, it would be fair to give the nightmare all the abilities of a fiendish servant of a 15th character level blackguard.

 

[FireLance]

To follow up on my previous post, I've just checked Dungeon #100 and the feat replaces the blackguard's fiendish servant with a nightmare who gains all the abilities of a fiendish servant of the blackguard's character level.