Alright, so I've taken a look into this:
A character with some mixture of Paladin 5, Ashworm Dragoon 10, Beastmaster 1, Halfling Outrider 4, Devoted Tracker, and Natural Bond can give their Ashworm +20 HD, +24 NA, +12 Str, +3 Dex, and a mess of other nice things (like Evasion, Improved Evasion, and Share Spells).
That comes out to a 23 HD Huge Ashworm with Str 43, Dex 13, Con 21, Int 7, Wis 13, Cha 6, and +33 NA.
Now...
1) What's the best order for all of that?
2) I can shave off a level of Ashworm Dragoon and Halfling Outrider without any reduction in bonuses; any ideas for replacing those two levels? I'm in that awkward place where adding another level of Halfling Outrider won't do anything, so...
