Magmage (Magma sorcerer)

(I put also some other spells for compensating some aspects where magma sorceries don’t excel at and some just for the look of it XD)

Glintstone cometshard as a long range projectile option (because magma shot doesn’t travel too far and roiling magma and Comet costs way more)
Fire serpent from the DLC because even if not related with the great serpent in Gelmir, it’s still a cool incantation and the name fits (and costs only 11 fp)
Flame Fall Upon them reminds me of volcano boulders when it erupts and it has a wide area and good damage.
Flame Grant Me Strength and golden vow because they’re great buffs and help with damage output

Talismans

As you can already see I will briefly explain why I choose these ones:

Graven mass talisman boosts SORCERIES by 8%
Talisman of the Dread (DLC item) boosts all magma spells and skills by 15% (yes also magma blade and blasphemous blade but we don’t use them here)
Radagon Icon or Beloved Stardust (the latter is a DLC item) maximum casting speed is reached at 70 dex and these two talisman help with that, Radagon Icon gives 30 virtual Dexterity towards casting speed and Beloved Stardust gives you 99 but at the cost of -30% damage absorption, use what you find more comfortable with
Godfrey Icon boosts charged spells and skills by 15%

Skills and spells in the build AFFECTED by Godfrey Icon talisman:

Spells: Magma shot, Glintstone cometshard, Roiling magma, Fire serpent and Flame Fall Upon Them.
Skills: None
Skills and spells in the build NOT AFFECTED by Godfrey Icon talisman:
Spells: Rykard’s Rancor, Gelmir’s fury and of course FGMS and golden vow because they’re just buffs.
Skills: Rellana’s Twin Blades skill: Moon-and-Fire Stance

As you can already see we use this set of weapons:

Double Gelmir Glintstone Staff (you don’t need to upgrade both, just remember to cast with the one upgrade lol), of course, for a boost to magma sorceries by 15% each (so a 30% boost)
Rellana’s Twin Blades as a melee option (DLC boss weapon)and it’s a pretty strong weapon that scales well In both INT and FTH
Serpent Crest shield for a parry option against the most aggressive bosses (like Malenia or DLC final boss as you will not able to use spells as effectively against them, Maliketh too but you can parry only two attacks with a very specific item)
And lastly the Golden order seal for the incantations we use (yes it scales better compared to Gelmir staff but it’s not the focus of the build)

We use Morgott’s great rune for a 25% hp boost
Opaline Hardtear(duration: 3 minutes) for a 15% damage negation increase (it can help mitigating the drawback of beloved Stardust if you use it)
Flame-Shrouding Cracked Tear(duration: 3 minutes) for 20% fire damage boost (it stacks with flame Grant Me Strength which also boost fire damage by 20%)

This is mostly up to you but by the fact we don’t have much endurance you have to be careful not to reach heavy load

Maliketh: he is super aggressive in both phases so he counters pretty much the majority of casters.
Malenia: she’s aggressive especially in 2nd phase but with practice you can still cast spells against her.
Promised Consort Radahn: super aggressive in both phases he hard counters casters too (unless you use carian slicer).
Fire giant: mostly because of his high resistance to fire damage, use Glintstone cometshard and rellana’s Twin Blades one handed(so it uses the magic one) against him.
Mohg(the illusion in the sewer too): same as Fire giant, he has high resistance to fire damage.
Radagon: he can parry spells so use them to punish attacks when he can’t parry, other than that he’s weak to fire.
Magma wyrms: they are resistance to fire damage and the two in Gelmir region are straight up immune to it.
Rykard: not using serpent hunter against him is madness.
Man-Serpents: enemies in volcano manor that are immune to fire damage.