What is the best Polymorph form for a caster (to keep casting)?

Question

As in the title. I'm looking for a good form to choose for my caster to stay in. What I'm looking for specifically is:

• Need to be a form that can cast spells so I can also keep casting my spells while in this new form,
• Access to flying, so I don't need to cast Fly,
• Very good armor, so I can't get hit (at least not easily and not often),
• Good Physical Stats so I get the HP boost and Fort Save boost from CON, Armor boost and Ref Save boost from DEX,
• Anything else is a nice bonus but not necessary.

Character as of now as that has been asked for:

• Aasimar / Lesser Aasimar / Saint (which means Outsider, not that it matters as there is plenty of ways to become one temporarily), LA +2 removed with buyout,
• Double Progression Caster (Cleric and Wizard spell lists) ECL 13 (but CL 15 for Clr Spells and 16 for Wiz Spells),
• Has Incantatrix Metamagic Effect, so Polymorph will be a Persistent ordeal.

Currently I'm considering:

• Juvenile Brass Dragon, nice armor bonus, awesome speed (poor maneuverability though), decent physical stats and burrow movement as a bonus. Being a dragon itself is kind of a downside though, might be suspicious talking with people in such form and raising way too many eyebrows on the street.
• Astral Deva > Planetar, awesome armor bonus, decent speed (with good maneuverability), great physical stats, nothing as a bonus. It's a humanoid in shape, so apart from being large (which can easily be fixed with a level 1 spell) doesn't stand out too much and can wear regular clothes, thus look kind of natural.

Are there any better forms I should consider? As a bare minimum wildly better in some way while slightly worse in some other way? Goal is to make the character near-invincible, Polymorph is just a way to get decent stats cheaply.

DISCLAIMER: Only RAW, only official WotC sources. No Pun-Pun, Loops or Wish.

Answer 1

As you are ECL 13 character, but are looking at 14 HD planetar, I assume you are looking forvard to things which will become availale during few next levels.

You have already listed very stong options, so I don't think you may expect much. Horned devil is a classic and overall improvement to stats, but nothing special. It grants flight, but it is a joke compared to that of a planetar.

But I think you may gain more than stats from such a valuable resource as a polymorph effect. No thread which mentions optimization and polymorph can go without mention of dire tortoise. Lightning strike is an ability to act in the surprise round even if there is no surprise. It requires surogate spellcasting feat in your case, but it is worth it. Starting almost any fight first is enormous benefit. Tortoise itself has decent stats: good constitution and natural armor. Burrow speed is an ok bonus, but nothing special really.

Also, consider draconic polymorph for better forms. +8 strength is largely wasted for your character, but better forms may be more significant, than an additional spell level. Another thing to consider: persistent spell lists only personal and fixed ranges. Touch spells cast on yourself may very well count, but draconic polymorph eliminates any ambiguity on the subject.

Answer 2

Abeil are bee-people from Monster Manual 2. They are monstrous humanoids (thus valid forms for polymorph without needing to already be the relevant type). There are three castes of abiel--vassal, soldier, and queen. The vassal isn't much use, it's really just going to give you a fly speed.

Abeil - Soldier Caste, however, is a large sized creature with a 90' (good) fly speed, Improved Grab, two claws and a strength-damaging poison sting, but perhaps more relevantly, has Str 22, Dex 13, and Con 16.

The Queen Caste of Abeil is similar, but medium size, and 18 str, and their poison is weaker. The actual monster has spells, but for purposes of polymorph, the Soldier is better. Unfortunately, neither gives natural armor.

The first thing I'd suggested in my original answer was a templated troll. While the templates are not an option, Troll is still not a bad idea. It has 23 str, 14 dex, 23 con, +5 natural armor, and it can cast spells (provided you're not using the late-3.5 polymorph subschool).

But, that doesn't allow you to fly.

Another thing to possibly consider is taking the feat Assume Supernatural Ability, from Savage Species. It allows you to select a single supernatural ability from a specific form you can magically take, and gain that ability in that form. It does, however, apply a -2 penalty to all your d20 rolls when using it, and in stressful situations (such as combat) you have to make a will save to actually be able to use the ability. However, if you took it and used Soldier-caste Abiel, they have a supernatural special attack called Stormwing that would allow you to take a full-round action to make a 40-foot radius 6d6 sonic damage attack in flight once per 1d4 rounds.

I want to see if I can find a better form that gives natural armor and flight, along with comparable ability scores, but for now soldier-caste Abeil may be a very good option.