D&D 5E Quick way to make Legendary Monsters

[77IM]

I've developed a quick system of Legendariness to turn any standard monster into a semi-legendary monster (similar to 4E's Elite and Solo classes).

Legendariness	Legendary Actions	Legendary Resistance	Proficiency increase (attacks, saves, skills, save DCs)	Hit Points	XP
Rare	1 (1/round)	1/day	+1	x2	x2
Very Rare	2 (2/round)	2/day	+2	x3	x3
Legendary	3 (3/round)	3/day	+3	x4	x4

Examples:

The rare salamander noble has 180 hit points, an attack bonus of +7, legendary resistance 1/day, and 1 legendary action: make a tail attack. 3,600 XP

The rare thri-kreen champion has 66 hit points, attacks of +4, legendary resistance 1/day, and 1 legendary action: leap up to 30 feet and make a claw attack. 400 XP. (The legendary action incorporates movement because it's more interesting and because the claw attack ain't that great.)

The very rare ankheg queen has 117 hit points, and has an attack bonus of +7 and her acid spray DC is 15. She has 2/day legendary resistance, and 2 legendary actions: automatically damage a grappled creature; spray acid (costs 2 actions). 1,350 XP. (The grapple damage is automatic because it requires her to have already grappled a creature first.)

The legendary Grimlock High King, who is said to dwell so deep in the underdark that sunlight has never shone in his throne room, has 44 hit points, +8 to hit and a Passive Perception of 16 (pretty decent for an NPC), 3/day legendary resistance, and 3 legendary actions: make a single attack; search; move his speed and then hide. 200 XP. (The move+hide is 1 action because even when they are combined it's pretty hard for him to use, plus he has no ranged attacks so it's not such a great move in general.)


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At a high level, the system is meant to simulate fighting multiple creatures, which is why the hit points and XP are a simple multiplier. It's similar to the Angry GM's double/triple/quadruple creatures, but less literal because the legendary actions are spread over the life of the creature and the legendary resistance can kick in whenever you need it to. Plus you can get creative with the Legendary Actions, to make the fight more interesting and reinforce the monster's signature traits.

I have no idea how well this jives with the DMG's guidelines on creating monsters, and applying it to certain creatures in the Monster Manual produces weird results. For example, applying these rules to a young dragon typically produces a creature with way more hit points than an adult dragon, but less damage output. It was more important to me that the system be simple enough to apply on-the-fly.

What do you guys think?

 

[Croesus]

Not having used the system, I can't comment on how balanced it is, but I love the simplicity. My only concern is hit points. You're doubling the average HP, which include CON bonuses, which can lead to some huge HP totals. You might consider instead:

Rare: Max HP
Very Rare: x1.5 Max HP (including CON bonuses)
Legendary: x2 Max HP (including CON bonuses)

Example:
Rare Salamander has 144 HP vs. your 180 HP
Very Rare Salamander has 216 HP vs. your 270 HP
Legendary Salamander has 288 HP vs. your 360 HP

 

[77IM]

Well, the idea was, if you fought 2 salamanders they'd have a combined 180 HP, 3 salamanders would have 270 HP, etc.

But, a single creature only takes damage from area attacks once, and now you've got me wondering if that's enough of a factor in combat that the hit point increase should be less than a multiple. This is more of a concern with Very Rare and Legendary creatures since they are more likely to be fought Solo or with very few minions -- the Rare creatures are meant to be like Elites where they are part of an encounter with a bunch of other enemies (and so they might be hit with area attacks).