Trying the hardest one atm: SMN.
Note, it'll have absolutely no leveling progression plan.
1. Bio - 15s DoT, instant
2. Miasma - 24s DoT, casted
3. Summon - Summons a pet, pet summoned depends on how much Aethertrail you have at this point (none: garuda, 1, ifrit, 2, titan, 3, demi-bahamut), 30s cooldown, off-gcd
4. Aetherflow - Consume all aethertrail to let your pet use it's signature attack, grants 3 stacks of aetherflow and restores 20% MP. 60s cooldown. (if used without a target, your pet will do nothing)
5. Ruin - 1.5s cast
6. Ruin II - 2.5s cast, heavy MP cost outside dreadwyrm trance, higher potency than ruin.
If your pet crits, Ruin will upgrade to ruin III, which is instant cast and has increased potency (same as ruin 2)
7. Dreadwyrm Trance: Requires 3 aethertrail, increases damage by 15% for 15s, applies both DoTs (with damage increase applied) on the target, decreases MP cost of ruin II, turns into Deathflare, 40s cooldown. Deathflare cancels DWT, 400 potency AoE without fall-off.
8. Fester: 140 potency per DoT on the target, now includes pet DoTs, uses aetherflow stack, grants aethertrail, 23s duration. 10s cd
9. Painflare: 200 potency AoE, uses aetherflow stack, grants aethertrail, 23s duration. 10s cd
10. Bane: Spreads DoTs to nearby targets, uses aetherflow stack, grants aethertrail, 23s duration. 10s cd
11. Southern Cross: 2.5s cast, 3 targets (primary + 2 random within 7y range), applies a 50 potency AoE with a radius of 3y around each of them. (zurvan skills are allowed, right?)
Signature attacks (on aetherflow cast):
Garuda: AoE damage + magic vuln
Ifrit: AoE damage + 30s DoT
Titan: AoE damage + 10s DoT
Demi-bahamut: Ahk morn
12. Pet action (just 1 instead of 3 per pet):
Garuda: Contagion, extends dot durations by 15s
Titan: Party-wide 7% damage taken reduction for 10s.
Ifrit: Extends all detrimental effects on the target by 3s (really.. all, also from other players, so including trick attack).
Demi-bahamut: Ruination: increases potency of ruin attacks by 25%.
All 60s cooldown, not shared.
Titan will do AoE damage on auto-attacks.
Not exactly 12 actions, but it's on 12 buttons. It has some line-up stuff to worry about, aethertrail timer back and even more tight to compensate for having to track less cooldowns, and for the AoE spam, selecting the correct target is really important.