Fighter Subclass: Crusader [5e]

A Crusader is a fighter whose devotion to their deity manifests in divine power. Their powers are less expansive than a cleric's, but they are able to combine their martial talents and clerical spells. 

SPELLCASTING 

When you reach 3rd level, you augment your martial prowess with the ability to cast spells. See chapter 10 for the general rules of spellcasting and chapter 11 for the cleric spell list. Cantrips. You learn two cantrips of your choice from the cleric spell list. Vou learn an additional cleric cantrip of your choice at 10th level. 

Domain Selection. All Crusaders choose a single domain. This forms the backbone of their spellcasting, as well as many of their subclass abilities. Spell Slots. The Eldritch Knight Spellcasting table (PH 75) shows how many spell slots you have to cast your spells of 1st level and higher. To cast one of these spells, you must expend a slot of the spell's level or higher. You regain all expended spell slots when you finish a long rest. For example, if you know the 1st level spell Cure Wounds and have a 1st level and a 2nd level spell slot available, you can cast shield using either slot. 

Spells Known of 1st-Level and Higher. At 3rd level, you know the 1st level spells from your domain, plus one of choice from the cleric list. At 7th, 13th, and 19th levels, you add the spells of your domain for the new level of spell slots you acquire at that point. At 5th, 10th, 15th, and 20th, another cleric spell may be chosen. Whenever you gain a level in this class, you can replace one of the cleric spells you know (but not one of the domain spells) with another spell of your choice from the cleric spell list. The new spell must be of a level for which you have spell slots. 

Spellcasting Ability. Wisdom is your spellcasting ability for your cleric spells, since you gain your spells through devotion and prayer. You use your Wisdom whenever a spell refers to your spellcasting ability. In addition, you use your Wisdom modifier when setting the saving throw DC for a cleric spell you cast and when making an attack roll with one. 

Spell save DC + 8 + your proficiency bonus + your Wisdom modifier 

Spell attack modifier = your proficiency bonus + your Wisdom modifier 

Domain Abilities: At 3rd level, you gain the 1st level abilities of your chosen Domain. Those domains that grant proficiency with martial weapons and/or heavy armor do not gain additional advantages. 

Weapon Focus: At 7th level, you may chose a two specific weapons, or a weapon and a shield, and bond them as spellcasting foci. You may cast spells as if with a focus when using either of these items. Bonding these items requires a one hour ritual, during which the item must be within your reach the entire time. In addition, you may cast any cleric spell you know as a ritual if it has the ritual tag. 

Enhanced Domain Abilities: At 10th level, you gain the benefits of the 8th level ability of your chosen domain. 

Spell and Blade: At 15th level, when you make an attack action, you may cast a Cantrip or 1st level spell, using no more than a 1st level spell slot, as a bonus action. 

Divine Intervention: At 18th level, you may attempt divine intervention as a cleric. Your chance of successfully invoking divine intervention is equal to one-half your fighter level, plus any cleric levels, and your Wisdom modifier. As with clerics, if you are successful, you may not use this feature for another 7 days. 

Design notes: This is explicitly a fighter/cleric, a divine version of the Eldritch Knight. While the Eldritch Knight finds their spells limited largely to two schools, the Crusader finds theirs primarily limited by their Domain. Since they do not get Channel Divinity, several of the domain powers don't apply, and they're gain these abilities two levels later than the equivalent cleric. This is a choice. 

3rd level: They cast spells. Like Eldritch Knights and Arcane Tricksters, they begin unable to use foci, limiting them as spellcasters. 

7th level: This grants them Foci, though somewhat more limited than a cleric who can just pick up a holy symbol; the Crusader must choose and bond with specific items. This is a bit less impressive than a Eldritch Knight's "summon your weapon to you", so included the ability to cast spells they know as rituals, if the spells themselves are rituals. 

10th: 8th level domain abilities. Didn't see anything that got broken by throwing these in. 

15th level: This is related to the Eldritch Knight's War Magic (7th) and Improved War Magic (18th). Because it as Attack-to-Cast, this is slightly better in a fighter's hands (since using the Attack action allows them to take additional attacks), which is why it is limited to cantrips and 1st level spells, whereas WM allows just cantrips, and IWM allows any spell. 

18th: Another "cleric lite" ability. At 18th level, they may be (are likely) better than a 10th level cleric, as their chance it 9 + Wisdom modifier (so, equal to a 10th level priest if they have a +1), and they can, at most, be equal to a 15th level priest (20th level fighter + 5 from a 20 Wisdom).