Please stop suggesting a charm based Sorcerer. Everyone in your group will hate you.
Acolyte of the Skin I:
You replace your own skin with a demon's one. You gain IMMUNITY to poision, +2 Con, 10 Fire Resistance, +2 Dodge and 2 Cold/Electric/Acid/Sonic Resistance. You gain +1 Max caster level and caster level to your fire spells. You summon the essence of a demon and are now able to cast Demonic rays Spell as SLA.
- Demonic rays Spell: You emanate two rays from your eyes on one target. Each of them deals 1d3 per caster level, up to a maximum 15d3 at caster level 15. Cooldown 6 seconds.
Acolyte of the Skin II:
An acolyte’s skin and its wearer have grown more comfortable together, as if they had never been separate. You gain IMMUNITY to Disease, +2 Con (+4 total), 10 Fire resistance (+20 total), another +2 Dodge and 2 Cold/Electric/Acid/Sonic Resistance (+4 total). You gain +1 Max caster level and caster level to your fire spells. You are now able to cast Demonic Roar as SLA.
- Demonic Roar: You roar like you never had in your whole life. You deal a 6d6 fire damage and your opponents become Shaken and Helpless for 2 seconds. This affects everything, including Undeads and Constructs. DC: 15 + Half character level + Cha Modifier + Fear based effects enhancements (the one in Draconic for example). AoE same as Haste and Daunting Roar. Cooldown 10 seconds.
Acolyte of the Skin III:
An acolyte's skin and its wearer are now the same entity. You gain Immunity to Blindness, +2 Con (+6 total), 10 Fire resistance (+30 total), +2 Dodge (+6 Dodge), +2 Cold/Electric/Acid/Sonic Resistance. You gain +1 Max caster level and caster level to your fire spells. Only the final death can separate you two. You also gain 25 DR/- . Your affinity with Fire is now at the maximum level. You also gain 20 Fire Spell power. You are now able to cast Demonic Fireball as Sla.
- Demonic Fireball: You create a powerful ball of demoniac fire with your mouth. On impact, the explosion deals 1d3+1 fire damage per caster level, up to a maximum of 30d3+30 at Caster Level 30. This spell is too powerful for you and you need some time to heal your wounds. You suffer a -2 Con penalty lasting 6 seconds. AoE same as Delayed Blast Fireball. Cooldown 8 seconds.
To summarize, you will have:
30 Fire Resistance,
6 Dodge,
6 Element resistance
3 MCL/CL to Fire spells
Immunity to Blindess/Poision/Disease
+6 Con
25 DR/-
+20 Fire Spell power.
And the 3 SLAs that I've just made up.
As you can see. this PrE is more defensive than offensive so most of these bonuses are written to achieve that goal. This PrE is for more survavibility hence why the Stun SLAs at tier two. However, being a demon, I feel also that we wouldn't be a real demon without a powerful offensive SLA. Being kinda powerful, the cooldown at tier 3 is 8 seconds, making it not really spammable. Can be increased to 10 seconds but then it would have the same cooldown as the stun.
The Tier 1 SLA is basically a Lightning bolt of fire but single target, so worse than it in the end.
The Tier 3 is an enhanced Delayed Blast Fireball, capped at caster level 30. You also suffer a -2 Con when you cast it. Being powerful has some consequences.
I didn't include a summon at tier 3 because Turbine just can't make them useful. It would just be a waste of time and a waste of PrE.