Hey guys I made a 9th level holy spell let me know any feedback you have 

https://www.dndbeyond.com/homebrew/creations/view?entityTypeId=1118725998&id=3118582

This part makes no sense: "The creatures take 1/4 damage except undead, fiends and aberrations they take regularly damage no half or double on a successful save." It seems to say that material plane enemies take 1/4 damage, but then they take "regularly damage no half or double on a success", which is thoroughly incomprehensible.

I changed it a little but what I was saying was that creatures who saved on the dc only take 1/4 damage but if that creature is a undead, fiends or aberrations they take the regular amount of damage with no reduction or additional damage instead of the regular 1/4 damage taken all other creatures take 

So, if the Fiends, Undead, and Aberrations in a 50-foot radius take 17d8 Fire Damage, 7d10 Radiant Damage and 7d6 Psychic Damage (I assume you misspelled Psychic) doubled.

I think you are trying to play off of 777 with the damage dice.

First, I believe spells at least tend to use the same damage die. See, Meteor Swarm and Flame Strike

If the spell target has more than 100 HP, this spell is better than Power Word Kill by a wide margin. Also, it averages 139.5 damage or 279 damage against Aberrations, Fiends, and Undead. Plus, it has a rider effect of creating Difficult terrain. Meteor Swarm has a similar effect (technically a shorter range but a larger AoE) and deals an average 140 damage.

Some changes I would make:

• Duration: 1 minute.
• Range/Area: 1 mile (50 foot Radius sphere)
• You point to an area in range and a giant flame burst from the floor with a holy glow in a 50ft radius. Creatures you choose in the area when the spell is cast must make an Intelligence save or take 7d8 Fire Damage, 7d8 Radiant Damage, and 7d8 Psychic Damage or half as much on a successful one. Aberrations, Fiends, and Undead take double damage on a success or failure.
• For the duration, the area is difficult terrain for Aberrations, Fiends, and Undead creatures.

I feel like Aberrations, Fiends, and Undead doesn't really limit the spell that much so it's just a super high damage nuke. Toning it down makes it more reasonable in my opinion. In addition, rewriting it to allow for a save for half damage causes it to interact with features like Evasion (if there is an equivalent for Intelligence saves). As an AoE that deals damage, I would expect this to require a Dexterity Save instead of Intelligence, but I left it. A Wisdom save may also be interesting. Also, Aberrations, Fiends, and Undead taking double damage on a successful save and normal damage on a successful one is the same as taking half damage on a successful save but the damage is always doubled. If you want to make the spell more reliable without pumping up the damage, you could also add "if a target is immune to any of the damage from the spell, it is resistant instead" or "This damage can't be reduced or prevented in any way", possibly restricting this to Aberrations, Fiends, and Undead.

This version averages 94.5 on average for general targets with 47.25 on a successful save. Against Aberrations, Fiends, and Undead, it averages 189 on average with 94.5 on a successful save.

What do you think of these suggestions?