I thought about making this a Wizard sub-class, but gave Sorcerer a try. I'm afraid it is OP because Sorcerers don't get any summoning spells. I'm guessing there is a reason that I'm not seeing for that.
Sorcerer Origin
Different sorcerers claim different origins for their innate magic. Many variations exist, yours come from a pact made with an Aberration, an Elemental, or an Ooze.
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Level 1
Summoning Spells
You learn additional spells when you reach certain levels in this class, as shown on the Summoning Spells table. Each of these spells counts as a sorcerer spell for you, but it doesn't count against the number of sorcerer spells you know.
All of your summoned creatures have the statistics of the chosen form, but they are an Aberration, an Elemental, or an Ooze, depending on your origin.
You can use your innate magic to heal your summoned creatures. As a reaction, you can spend 1 or more Sorcery Points to heal your summoned creature for (proficiency bonus) health points per Sorcery Point spent.
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Level 4
Sorcerous Versatility (TCoE 66)
Whenever you reach a level in this class that grants the Ability Score Improvement feature, you can do one of the following, representing the magic within you flowing in new ways:
Replace one of the options you chose for the Metamagic feature with a different Metamagic option available to you.
Replace one cantrip you learned from this class's Spellcasting feature with another cantrip from the sorcerer spell list.
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Level 5
Magical Guidance (TCoE 66) [modified]
You can spend 1 sorcery point to roll an ability check with advantage.
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Level 6
Sorcerous Enhancement
(based on Undead Thralls, PHB 119)
Your summoned creature's attacks count as magical for the purpose of overcoming resistance and immunity to non-magical attacks and damage.
Your summoned creature's hit point maximum is increased by an amount equal to your Charisma modifier plus your Proficiency Bonus.
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Level 14
Sorcerous Steed
(based on Revelation in Flesh, TCoE 68)
When you cast Phantom Steed, your steed becomes a Sorcerous Steed, gaining the following traits:
Your Sorcerous Steed gains a flying speed equal to your walking speed, and it can hover.
Your Sorcerous Steed gains a swimming speed equal to twice your walking speed.
Your Sorcerous Steed can breathe air and water.
While you are riding your Sorcerous Steed, you can also breathe air and water.
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Level 18
Herd of Sorcerous Steeds (based on Wind Soul, XGtE 52)
When casting Phantom Steed, you may spend Sorcery Points to summon more than one Sorcerous Steed. 1 Sorcery Point per additional Sorcerous Steeds. Any humanoid of your choice can ride a Sorcerous Steed. Anyone riding one of your Sorcerous Steeds can breathe air and water.
So first you are missing a “L” at the end of celestial, you wrote it “celestia”. The sorcerous healing is good at low levels but it’s really not going to do much later, overall I think it’s really cool, oh forgot to mention: why would I ever use the level five ability? Why would I purposefully role with disadvantage? Unless you add a ability that gives you some sort of “bonus” for rolling with disadvantage.
1. gain the ability to add you charisma modifier to your constitution saving throw when making the save for summon spells.
2. Gain proficiency in medium armor and whips. Whips are also a spell focus for summon spells.
3. Find familiar can be cast with no spell components and use 1 sorcerer point.
4. Increase the healing to sorcerer level+ charisma modifier. Use proficiency bonus per short rest.
5. Twin casting meta magic works on summon spells. (If it doesn't already) and gain this meta magic but can only be used for summon spells. (When using this feature, you shorten the duration to one minute and the twin cast count as one concentration spell)
I thought about making this a Wizard sub-class, but gave Sorcerer a try. I'm afraid it is OP because Sorcerers don't get any summoning spells. I'm guessing there is a reason that I'm not seeing for that.
Sorcerer Origin
Different sorcerers claim different origins for their innate magic. Many variations exist, yours come from a pact made with an Aberration, an Elemental, or an Ooze.
---
Level 1
Summoning Spells
You learn additional spells when you reach certain levels in this class, as shown on the Summoning Spells table. Each of these spells counts as a sorcerer spell for you, but it doesn't count against the number of sorcerer spells you know.
All of your summoned creatures have the statistics of the chosen form, but they are an Aberration, an Elemental, or an Ooze, depending on your origin.
Character Level
Spells
1
Find Familiar
3
Summon Beast
5
Summon Fey
Summon Shadowspawn
Summon Undead
Phantom Steed
7
Summon Aberration
Summon Construct
Summon Elemental
9
Summon Celestia
Sorcerous Healing
You can use your innate magic to heal your summoned creatures. As a reaction, you can spend 1 or more Sorcery Points to heal your summoned creature for (proficiency bonus) health points per Sorcery Point spent.
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Level 4
Sorcerous Versatility (TCoE 66)
Whenever you reach a level in this class that grants the Ability Score Improvement feature, you can do one of the following, representing the magic within you flowing in new ways:
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Level 5
Magical Guidance (TCoE 66) [modified]
You can spend 1 sorcery point to roll an ability check with advantage.
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Level 6
Sorcerous Enhancement
(based on Undead Thralls, PHB 119)
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Level 14
Sorcerous Steed
(based on Revelation in Flesh, TCoE 68)
When you cast Phantom Steed, your steed becomes a Sorcerous Steed, gaining the following traits:
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Level 18
Herd of Sorcerous Steeds (based on Wind Soul, XGtE 52)
When casting Phantom Steed, you may spend Sorcery Points to summon more than one Sorcerous Steed. 1 Sorcery Point per additional Sorcerous Steeds. Any humanoid of your choice can ride a Sorcerous Steed. Anyone riding one of your Sorcerous Steeds can breathe air and water.
So first you are missing a “L” at the end of celestial, you wrote it “celestia”. The sorcerous healing is good at low levels but it’s really not going to do much later, overall I think it’s really cool, oh forgot to mention: why would I ever use the level five ability? Why would I purposefully role with disadvantage? Unless you add a ability that gives you some sort of “bonus” for rolling with disadvantage.
It honestly seems weak.
Things to consider:
1. gain the ability to add you charisma modifier to your constitution saving throw when making the save for summon spells.
2. Gain proficiency in medium armor and whips. Whips are also a spell focus for summon spells.
3. Find familiar can be cast with no spell components and use 1 sorcerer point.
4. Increase the healing to sorcerer level+ charisma modifier. Use proficiency bonus per short rest.
5. Twin casting meta magic works on summon spells. (If it doesn't already) and gain this meta magic but can only be used for summon spells. (When using this feature, you shorten the duration to one minute and the twin cast count as one concentration spell)