Looking back at the original text, I think we've got quite an abundance of mutations already (it seems there should be 20% with planar travel and only 1% for everything else), so I think we don't need mutations that stack at all (ie, there shouldn't be multiple mutations and certainly not 3 of them at a time). So I'll propose (with rejiggering probabilities and adjusting numbers to match caveling/troll mutate better):
1-5 - Mass Plane Travel - functions like a 1/week plane shift, except the kobalt can shift itself and up to 40 other kobalts between two Prime Material planes. Caster level X. The kobalt gains a +4 racial bonus on Charisma and a +4 racial bonus on Diplomacy checks against other kobalts. Its LA increases by 1.
6 - Carapace - Increase natural armour by +2
7 - Vomit Acid - 1/day. 20 ft. line of acid doing 2d4 damage, Con-based Reflex save for half.
8 - Extra Arm - Gives an additional off-hand attack.
9 - Claws - Each hand can do 1d3 claw damage.
10 - Long Legs - Increase base land speed by 5 feet.
11 - Whiplike Tail - Secondary tail slap attack for 1d6 damage with 1.5 times Strength bonus.
12 - Redundant Organs - The kobalt's extra organs grantslight fortification (25% chance to negate critical hit).
13 - Acid Blood - Deals 1d4 points of damage to any creature attacking it with a slashing or piercing weapon who fails to succeed at a Reflex save. The save DC equals 10 plus the kobalt's Con bonus.
14 - Strong - +2 racial bonus to Str.
15 - Agile - +2 racial bonus to Dex.
16 - Tough - +2 racial bonus to Con.
17 - Smart - +2 racial bonus to Int.
18 - Zen - +2 racial bonus to Wis.
19 - Strong Willed - +2 racial bonus to Cha.
20 - ??
21-100 - No mutation
I'm not sure planar travel requires the +4 to Cha, though the bonus on Diplomacy is good. What if we just made it a +4 circumstance bonus to all Cha-based checks against other kobalts?
I'm also not sure I like the plain ability score bonuses. They're boring.![]()
I like all that. Freyar?
Their Infravision allows them to see any heated body at up to 60 meters (66 yards) at night or in darkness of any kind. They may detect the slight warmth that plants emit and find places on the ground where beings rested within the last hour; this latter ability allows them to track parties at night with 90% accuracy.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.