Vassal of Bahamut

[Anthrowhale]

Be a Neraph and pay(1.35K) for PAO[Horned Devil] to reach AC 35. Use a Hat of Disguise (1.8K) to appear as something more innocuous. As a Baatezu, you inherit Immunity to Fire and Poison from your type.

For feats, take Assume Supernatural Ability[Infernal Wound].

Boost your AC via a +1 Mithril Chain Shirt, Dastana, and a +1 Mithril Steel Shield (5K in total) to reach AC 43. The dragon now has a rather low probability of hitting.

With a strength of 31 and BAB+7 vs AC 24, you can typically hit.

Get a composite[10] longbow+1 so you have a ranged attack dealing 1d8+11 with an attack bonus of 15=7(bab)+7(dex)+1(magic) that typically hits.

Find the lair of the red dragon and start taking it's treasure. They hate that so it's sure to attack. Use weapons to deal with minions and target the red dragon with the bow at range. It's almost sure to try a breath weapon, but you are immune via type. Failing minions and breath weapon, it's likely to go for a physical attack. Most physical attacks will miss due to AC 43 and you'll have a chance to attack back in melee. If you hit just once with the tail attack (45% chance as a secondary natural attack), it begins to bleed at 2hp/round and must make a DC 24 heal check to end the bleeding. If the Red Dragon does not have the heal skill (likely) it will surely die in a few minutes, or faster if it chooses to stay in melee range.