Cultist (Rogue subclass)

[mcumoric]

Cultist
Cultists are rogues who worship dark gods. They are evil most of the time, though they aren't always evil.

Sacrifice
Starting at the 3rd level, you may use a bonus action to declare a creature, your sacrifice. For the next minute every attack you make against that creature adds your sneak attack unless you have disadvantage and has a +1 to attack and damage rolls. If you reduce your sacrifice to 0 hit points before the minute ends, roll your sneak attack dice. You regain a number of hit points equal to your roll. You may use this ability a number of times equal to your wisdom modifier per long rest.

Dark gift
Starting at the 3rd level, you learn how to cast arcane spells. You can choose spells from the warlock and cleric spell lists. You gain spells at certain levels determined by the table below.
Level - Cantrips known - Spells known - 1st slots - 2nd slots - 3rd slots - 4th slots
3rd - 2 - 3 - 2
4th - 2 - 4 - 3
5th - 2 - 4 - 3
6th - 2 - 4 - 4
7th - 2 - 5 - 4 - 2
8th - 2 - 6 - 4 - 2
9th - 2 - 6 - 4 - 2
10th - 3 - 7 - 4 - 3
11th - 3 - 8 - 4 - 3
12th - 3 - 8 - 4 - 3
13th - 3 - 9 - 4 - 3 - 2
14th - 3 - 10 - 4 - 3 - 2
15th - 3 - 10 - 4 - 3 - 2
16th - 3 - 11 - 4 - 3 - 3
17th - 3 - 11 - 4 - 3 - 3
18th - 3 - 11 - 4 - 3 - 3
19th - 3 - 12 - 4 - 3 - 3 - 1
20th - 3 - 13 - 4 - 3 - 3 - 1

Your spellcasting modifier is determined by your wisdom modifier.
Spellcasting modifier: your wisdom modifier.
Spellcasting save dc: 8 + your proficiency bonus + your wisdom modifier.
Spellcasting attack modifier: Your proficiency bonus + your wisdom modifier.

You may use a weapon as your spellcasting focus.

Dark devotion
Starting at the 3rd level, you gain advantage on saving throws against being charmed and frightened.

Eldritch advance
Starting at the 9th level, if you use an action to cast a cantrip you may use a bonus action to make a weapon attack.

Horrid knowledge
Starting at the 13th level, your horrid knowledge lets you summon sheds of your deity to damage the mind of your foes. As a bonus action you can force an enemy to make a wisdom saving throw versus your spell save dc. On a fail they take 3d4 psychic damage and are knocked prone. This increases by another 1d4 (4d4) at the 17th level.

Blackened heart
Starting at the 17th level, when you hit a creature with a melee weapon attack, you can use a bonus action to make a separate magical attack. Make a melee spell attack against your target, which on a hit, you deal necrotic damage equal to your sneak attack dice.

[JNAProductions]

Sacrifice is, in practice, gonna be a +1 to-hit and damage against a big target. It won't break anything, but it's not very thematic or fitting with 5E's design.

Dark Gift has casting drawn from a REALLY GOOD list (Cleric) and an okay list with a few stand outs (Warlock). I would definitely not give them full access to two full casters' lists.

Dark Devotion is good-combined with casting and Sacrifice, almost certainly too much for level 3.

Eldritch Advance is way too good. When an Eldritch Knight gets "Cantrip and one Attack," it's good for a few levels because one cantrip plus one attack is better than two attacks, especially with the SCAG cantrips, levels 7-10. But at level 11, it really loses its effectiveness, since three attacks will almost always be better than one attack plus one cantrip.
Rogues don't get multiple attacks. You're effectively adding the entirety of a cantrip's damage to your one attack.

Horrid Knowledge needs a range.

Blackened Heart is just bonkers. At the level you get it, that means you can consistently do 19d6+5 damage in melee range, assuming you get Sneak Attack and are using a nonmagical shortsword. (If you miss with the first attack, you've got a second shortsword-swing again and get your 10d6 at least.)

For reference, a Fighter can expect to do, at level 17, 6d6+15 at full accuracy, or 6d6+45 at -5 to-hit. 71.5 is what you do, on average, as compared to a Fighter's 36 (full accuracy) or 66 (GWM on).

[Amechra]

If I'm reading Sacrifice correctly, it's absolutely insane. Normally, you can only add your sneak attack damage to one weapon attack (with very particular weapon restrictions) per turn, but Sacrifice just flat-out applies it to any attacks you make for that minute.

A 5th-level Cultist casting Eldritch Blast against their Sacrifice would deal 2d10+6d6+2 damage if both attacks hit. That's... kinda absurd, and it only gets stronger. By the time you hit 17th level, you can just flat-out deal 4d10+36d6+4 damage with a single casting of Eldritch Blast. That's enough damage to solo an Ancient Red Dragon in four turns, going by average damage rolls.

I'm... assuming that that wasn't the intent? If so, you probably want to copy the wording from the Inquisitive's Insightful Fighting: "You can use your Sneak Attack against that target even if you don't have advantage on the attack roll, but not if you have disadvantage on it."