Essence of Brian (Legendary Boon)

Using your magic, you can create a bridge for Brian to enter a vessel you have prepared. As a Bonus Action, you may allow Brian to enter the body of one undead under your command for 1 minute or until damage leaves the undead creature at 0 HP, you use an action to recall Brian or you send Brian over to another undead creature. You can cause him to inhabit undead creatures an amount of times equal to your proficiency bonus. While Brian is inhabiting a creature, it gains the following benefits:

• Instinctive Nimbleness. The undead vessel gains a bonus to its AC and saving throws of +4 and its speed increases by 15 ft.
• Heroic Sacrifice. When Brian sees a creature make an attack against an ally, the vessel may use its reaction to move up to its speed towards the ally or the attacking creature and if it ends up within 5 feet of either, may make itself the target of the attack.
• Legendary Influence. The vessel can take 1 legendary action, choosing from the options below. Only 1 Legendary action can be taken at a time and only at the end of another creature's turn. The vessel regains its legendary action at the start of its turn.

-Disruptive strike. The vessel makes one of its melee attacks in its stat block, or it makes an unarmed strike, with a +2 bonus to hit and dmg. On a hit, the target reduces 2d6 from the next damage roll it makes before the start of its next turn.

-Flashy Flurry (once per inhabitation). The vessel replicates Brian's signature move from life. It lunges forward in a straight line up to 20 feet away, making a flashy pirouette. Each creature adjacent  to any space it passes by must make a Dexterity saving throw (DC 16) or take 3d8+4 slashing damage, taking half as much damage on a success.

(note: this is an experimental, campaign specific feature. And is not supposed to be treated as a normal feat)