[PF] Riding a giant toad/slug? Build idea and optimization help.

[Unbalanced]

So... Looking at a new character in the near future and exploring the option of a giant toad or slug riding (nevermind the Nauto-ness of that) character.
I'm thinking of a guy that comes from a far-away land where riding these sorts of creatures is fairly normal. Maybe even a semi-aquatic background. Wouldn't mind if he turns out to be a small character.
Don't want too much in the way of mounted combat though, want to be mainly melee combat fighting side-by-side with the mount. Preferably fighting with an axe and/or hammer.
Just looking for advice on optimizing a build with these things in mind...

Any advice appreciated.

[Infundibular]

There's always the Titanic Toad (MM2, under Titanic Creature), which could be funny just because it's size Colossal. Add some fun templates and hit the road and/or your enemies. I have no idea how you'd domesticate or ride one, but it would be hilarious. Talk to your DM about it. You could always have someone mind-control it.

[Dr. Yes]

Happily, Druid gets access to giant toads, giant frogs, and giant slugs as animal companions (http://www.d20pfsrd.com/classes/core-classes/druid/animal-companions). Of those, I would lean toward the frog for its ranged grapple. The toad's poison won't scale well, and the slug's DR looks nice until you realize that slashing and piercing account for most of the physical damage in the game. Notably, however, the slug does eventually become large on its own so that you don't have to be small to ride it.

[Unbalanced]

Happily, Druid gets access to giant toads, giant frogs, and giant slugs as animal companions (http://www.d20pfsrd.com/classes/core-classes/druid/animal-companions). Of those, I would lean toward the frog for its ranged grapple. The toad's poison won't scale well, and the slug's DR looks nice until you realize that slashing and piercing account for most of the physical damage in the game. Notably, however, the slug does eventually become large on its own so that you don't have to be small to ride it.

I saw druid as really being my only real option, however I was wanting to steer clear of magic users. Really wanted to excel in melee combat.
Was thinking more along the lines of a barbarian...
What are my options as far as being a melee combatant who wants a large, abnormal mount???

[Bhaakon]

Mad Dog (http://www.d20pfsrd.com/classes/core-classes/barbarian/archetypes/paizo---barbarian-archetypes/mad-dog) archetype barbarian gets access to the full Druid list of companions.

A beast rider cavalier also gets some abnormal mounts...eventually, but you'd need DM approval to get a frog, toad, or slug before 7th level.

In either case, you're probably going to want to go into the mammoth rider (http://www.d20pfsrd.com/classes/prestige-classes/other-paizo/i-m/mammoth-rider#TOC-Gigantic-Steed-Ex-) PRC at level 9.

[grarrrg]

What are my options as far as being a melee combatant who wants a large, abnormal mount???

First off, an Animal Companion is technically NOT the same thing as a Mount.
The two have a lot in common, and can stack in certain cases, but are still different things.

Next, the stacking, read this (http://paizo.com/paizo/faq/v5748nruor1fn#v5748eaic9qqn).

Long story short: if you want a crazy awesome X for a companion, you're going to have to be straight classes Druid or something with the Animal or Scalykind (technically also Sylvan Sorcerer, but you said Melee-ish, and I'll assume Eldritch Heritage is out).
OR Beast Rider Cavalier (http://www.d20pfsrd.com/classes/base-classes/cavalier/archetypes/paizo---cavalier-archetypes/beast-rider). There are no slugs/toads/etc... on the list, BUT the list says "Additional mounts might be available with GM approval."

Animal Domain comes with a -3 effective level penalty. Scalykind comes with a -2 (but limits your options to Snakes).

The Boon companion feat can give up to +4 effective level (up to your HD).

Classes that can get Domains, would be Cleric, Inquisitor, and Paladin (Sacred Servant (http://www.d20pfsrd.com/classes/core-classes/paladin/archetypes/paizo---paladin-archetypes/sacred-servant)), the Paladin comes with an additional -3 effective level penalty.
Theologian Cleric (http://www.d20pfsrd.com/classes/core-classes/cleric/archetypes/paizo---cleric-archetypes/theologian) counts as +2 levels for their Domain effects (doesn't get you them early, they're just more powerful).


Anywho...whichever way you go, see if you can get Mammoth Rider (http://www.d20pfsrd.com/classes/prestige-classes/other-paizo/i-m/mammoth-rider) allowed.
First level is a size boost to Huge, with the bonuses/penalties that that entails (STR/CON/Reach)
It's not so much the class that will be trouble, but the "special mount list".

EDIT: Stupid newer books and ninjas and whatnot...
Do the Barbarian thing. it gets full on Animal Companion Action.
Also, Mammoth Rider can be entered at 10th, qualified for at 9th. Generally worth it though.