Oath of Unwavering

As a Guardian, you gain abilities that bolster your defensive power and those of your allies. A Guardian's job is to protect the party from all harm, no matter the nature or source.

I wanted an AC boosting Paladin subclass for an NPC. The level 7 is a bit powerful, but I gave it a very situational level 15 to compensate. And have you seen Oath of Conquest?

Paladins who take the Oath of the Guardian are sworn to protect those in need, and provide safety in both body in mind. They do not shy from danger, and are not afriad to defy authority.

Tenets of the Guardian:

Fight the Corruption: It is your duty to ensure your charges are not tempted or corrupted by anything that seeks to harm them.

Protect the Vulnerable: You are enduring. It is your duty to shield the less so.

Redeem the Corrupted: If you are to fail an ally, you must protect them from themselves, so they may find themselves once more.

Keep the Vigil: You must be prepared to protect at any time. Those under your protection must rest safe.

Channel Divinity

At third level, if you have this oath, you gain the following Channel Divinity options.

Shielded Weapon: As a bonus action, you can expend a use of your Channel Divinity and imbue a weapon with protective magic. For the next 10 minutes, the bearer of the weapon gains a bonus to their AC equal to your proficiency bonus (PB).

Guard the Mind: As an action or reaction, you can expend a use of Channel Divinity to temporarily guard the mind of yourself or an ally. You touch a willing creature. For the next minute, that creature has immunity to psychic damage, resistance to thunder damage, and can't be frightened or charmed.

Aura of Warding

At 7th level, your very presence guards your allies from harm.

All allies within 10 ft gain +2 AC, so long as you aren't incapacitated.

This bonus increases to +3 AC at level 13.

At the 18th level, the range of this aura increases to 30 ft.

Protect the Veins

At 15th level, you gain the ability to cast Purify Food and Drink and Protect from Poison at will. For the purpose of this feature, these spells also apply to pathogen-based diseases.

Unwavering Champion

At 20th level, as an action, you can provide magical armor to all your allies. All allies within your Aura of Warding gain an unarmored AC of 16 + their DEX modifier. (The Aura of Warding bonus is added after Unwavering Champion is calculated).

This effect lasts 10 minutes, but once this feature is used, it cannot be used again until after you have taken a long rest.