Steal favor from the gods.
Some Rogues find their fortunes in the shadows where not even the gods could witness them. Some Apostates use their stolen divine power to establish their own cults, or simply go on to create an even larger fortune.

Level 3: Spellcasting

You have learned to cast spells.

Cantrips. You know three cantrips: Sacred Flame and two other cantrips of your choice from the Cleric spell list. Guidance and Thaumaturgy are recommended.
Whenever you gain a Rogue level, you can replace one of your cantrips, except Sacred Flame,with another Cleric cantrip of your choice.

Whenever you reach Rogue level 10, you learn another Cleric cantrip of your choice.

Spell Slots. The Apostate Spellcasting table shows how many spell slots you have to cast your level 1+ spells. You regain all expended spell slots when you finish a Long Rest.

Prepared Spells of Level 1+. You prepare the list of level 1+ spells that are available for you to cast with this feature. To start, choose three level 1 Cleric spells. Guiding Bolt, Detect Magic, and Command are recommend.

The number of spells on your list increases as you gain Rogue levels, as shown in the Prepared Spells column of Apostate Spellcasting table. Whenever that number increases, choose additional Cleric spells until the number of spells on your list matches the number in the Apostate Spellcasting table. The chosen spells must be of a level for which you have spell slots.

Changing Your Prepared Spells. Whenever you gain a Rogue level, you can replace one spell on your list with another Cleric spell for which you have spell slots.

Spellcasting Ability. Wisdom is your spellcasting ability for your Cleric spells.

Spellcasting Foucs. You can use a Holy symbol as a Spellcasting Focus for your Cleric spells.

Level 3: Stolen Flame

When you cast Sacred Flame, you can cast it as a bonus action, and you may opt to have the spell deal Necrotic damage instead of Radiant damage instead.

Level 9: Schism

You can attempt to steal the divine powers of a god temporarily, at great risk. As a Magic action, choose any Cleric spell of level 1 or lower. As part of the same action, you may cast that spell without expending a spell slot or material components. You can use this feature a number of times per long rest equal to your proficiency bonus. However, each use beyond the first in the same day strains your mortal form. After your first use, you must succeed on a DC 15 Wisdom saving throw each time you activate this feature. On a failure, you are knocked unconcious until the end of your next turn.

Level 13: Vowbreaker

You have learned the art of shattering the will of the divine in order to fuel your strikes.

When you hit with a Sneak Attack, you can expend a spell slot to gain additional Sneak Attack dice for use with your Cunning Strikes feature. The number of bonus Sneak Attack dice you gain equals twice the level of the spell slot expended. These bonus dice cannot be used to increase the damage of your Sneak Attack and may only be spent on Cunning Strikes effects.

Additionally, you can now choose any Cleric spell of level 2 or lower with your Schism class ability. If you would fail a save on this class feature, you become prone instead of unconcious.

Level 17: Mythtaker

You have hardened your resolve against the divine, and have learned how to turn their retribution into your own. Whenever you cast Sacred Flame on a creature that would qualify for a Sneak Attack, you may expend up to 3d6 to apply an effect from your Cunning Strikes.

Additionally, you can now choose any Cleric spell of level 3 or lower with your Schism class ability. If you would fail a save on this class feature, you may opt to gain 1 level of exhaustion instead of becoming prone or unconcious.