Regongar has the good fortune to have opted to pursue the path of the Magus, perhaps one of the most versatile (and dare we say, powerful?) classes in the game. Even better, he’s an Eldritch Scion, which uses his Charisma to power his spells (much like a Sorcerer). He’s also got a prodigious Strength score, making him competent in melee. The combination will allow him to buff up to protect himself while dishing out respectable damage.

It’s not all good news, however, as Regongar is Chaotic Evil, precluding the common tactic of dipping into Monk (Scaled Fist) for the Armor Class boost or Paladin for the ability to Smite Evil and gain a hefty bonus to Saves via Divine Grace. His Constitution and Dexterity are also fairly low, and he starts out with a dud feat - Combat Casting. Fortunately his starting spells are all decent, and his skills are the sort of thing we’d prefer to pick for our Magi, anyways.

All in all, he’s capable of mimicking The Tank reasonably well, and he’ll make use of a lot of the same staples that any character who aspires at front-line combat duty: Fighting Defensively, Crane Style, Crane Wing, Outflank, Dazzling Display and Shatter Defenses. While he can’t compete with a Magus protagonist, he’s honestly probably a better option than The Off-Tank… if you don’t mind having an evil companion, that is.

While the overall goal of the build (and many of the feats, skills and spell choices will remain the same), there are a few ways to build Regongar that work out well enough. First, and most simply, you can keep him as a Magus his entire run. He’ll do fine. But it seems like such a waste not to get four levels of Dragon Disciple to boost his Strength. He doesn’t really need more than fifteen levels in Magus, anyways - he can’t use the Dragonkind II spell his bloodline gives him, but the +3 Dodge Bonus to Armor Class he’ll gain as a 15th-level Magus is too good to pass up. This leaves one level leftover - might as well make use of another common build idea and dip one level of Alchemist (Vivisectionist) for the Sneak Attack damage and Mutagen.

Alternatively you can add levels of Eldritch Knight (you’ll need to boost his Knowledge (Arcana) up to rank 5 to qualify for this class), which will continue his Magus spell progression and give him a better Attack Bonus growth rate, but honestly, we prefer the class abilities on offer by the Magus and Dragon Disciple - the former will boost damage with Arcane Weapon Enhancement while the latter yields the aforementioned Strength bonus after four levels.