Giant Tidepool Dragon as Monstrous Mount

Prerequisite(s):
Arcana, Diplomacy, Intimidate, or Handle Animal 5 ranks; Ride 5 ranks.

Starting Statistics
Size Small; Speed 10 ft., fly 30 ft., swim 60 ft. (average; unable to carry a rider while flying or swimming); AC +3 natural armor; Attack bite (1d4); Ability Scores Str 15, Dex 11, Con 17, Int 8, Wis 14, Cha 14; Languages Common, Draconic; Special Qualities darkvision 60 ft., low-light vision, amphibious.

7th-Level Advancement
Size Medium; Speed 20 ft., fly 60 ft., swim 70 ft. (average; unable to carry a rider while flying or swimming); AC +2 natural armor; Attack bite (1d6); Ability Scores Str +4, Dex -2, Con +2.

Spell-Like Abilities (CL equal to HD)
3/day—tail strike, aqueous orb
4/day—slipstream, dousing rain, whispering wind, elemental speech
7/day—hydraulic push, obscuring mist, strong wings (self only), enlarge person (self only, the normal targeting restrictions of the spell do not apply)
at will—acid splash, dancing lights, detect poison, mage hand, touch of fatigue (DC 12)

10th-Level Advancement
Special Attacks: breath weapon (5-ft. line, 2d6 fire damage, Reflex DC [10 + 1/2 breathing creature’s racial HD + breathing creature’s Con modifier] for half, usable every 1d4 rounds)

11th-Level Advancement
Special Attacks: breath weapon range increases to 15-ft. cone

Mastery (7th Level)
The Giant Tidepool Dragon can carry a rider while flying or swimming, but reduces its fly or swim speed by half while doing so.

Unstable Breath Weapon
The Curse called Breath of Dagon twists the breath weapon damage:
d% | Behavior
01-25 | 5d6 cold damage to targets
26-50 | 5d6 lightning damage to targets
51-75 | 5d6 acid damage to targets
76-100| 5d6 negative energy damage to the breathing creature and everyone within 5-ft. (unpreventable)