For DMs looking for ideas on how they should homebrew legendary resistance mechanics, this document has a bunch of sample mechanics I have used in statblocks before.

• Adult Dragon: Breath Attack
  • The dragon has 3 legendary resistances and begins combat with 10 points of Charge. The dragon has a powerful breath attack which costs 10 points of Charge to use.
  • The player characters can see this glowing light building in its chest, and rising up its neck as it prepares the attack; they instinctively know that once the light reaches its jaws, it will be ready to fire again. This light represents the dragon’s Charge.
  • The dragon gains two stacks of Charge at the beginning of each of its turns, and gains an additional stack of Charge for each unspent legendary resistance it has at that time.
• Jin the Swordmaster’s Disciple: Deathrattle Haiku
  • Jin has 6 legendary resistances, which don’t do anything besides act as normal legendary resistances until Jin successfully hits a player with the Haiku Slash action.
  • The player hit by the Haiku Slash takes 0 damage from the attack instead of the listed damage, if Jin has any legendary resistances. Jin begins to compose a haiku, which will finish at the beginning of Jin’s next turn.
  • The player hit by the Haiku Slash can see splashes of ink floating around Jin’s body equal to the number of legendary resistances he has left. These splashes of ink are wiped away when their legendary resistance is spent.
  • If Jin has any resistances left at the beginning of his turn, he finishes the haiku, and the player instantly drops to 0 hp. If Jin runs out of resistances before finishing the haiku, then the player instead takes the damage from the slash as normal.
  • Jin can also lose a legendary resistances when he suffers enough damage in a single turn.
• Chronurgy Archmage: Perfected Precognition
  • The archmage has 3 legendary resistances, and begins combat with 2 points of Convergent Future.
  • The archmage’s resistances are represented by magical shards of glass which float around her and show possible futures. The shards dull when their legendary resistance is spent.
  • When the archmage sees another creature within 60 feet (including herself) make an attack roll, saving throw, or ability check, she can spend a point of Convergent Future to collapse the timelines and find one where that creature failed or succeeded.
  • The archmage can also spend a point of Convergent Future to prevent her spells from being counterspelled (even if no ability check is made), or cause a creature casting a spell within 60 feet to fail to cast the spell (still losing their spell slot).
  • The archmage gains a point of Convergent Future for every 5 cumulative unspent legendary resistances she has, which are tracked across turns (to a max of 2 points).
• The Sorcerer Supreme: Mana Syphon Engine
  • The sorcerer has 5 legendary resistances, and 20 sorcery points.
  • The sorcerer’s resistances are represented by a spinning glowing circle embedded in his chest.
  • Unspent legendary resistances turn into sorcery points.
  • The sorcerer can cast more than one leveled spell each turn, and can use as many metamagic options as he wants on each spell he casts.
• Elven Military Captain: Patience of the Ageless
  • The elf has 2 legendary resistances, which are represented by glowing notches on their extremely long sword.
  • The elf has a number of reactions each round equal to 1 + the number of unspent legendary resistances they have at the beginning of their turn.
  • The elf makes a number of attacks in their multiattack equal to 2 + the number of unspent legendary resistances they have at the beginning of their turn.
• Avourel Tarron, the Vengeful Archdruid: The Wilderness Walks as One
  • Avourel Tarron has a number of legendary resistances equal to the number of players in the party + 2; these resistances are represented by red flowers that bloom around his shoulders.
  • Avourel Tarron gains points of Savagery from unspent legendary resistances, up to a maximum of 5 points. These points can be spent to make the next spell he casts uncounterable, or to gain an additional legendary action this round.
  • Avourel Tarron has only one legendary action each round by default, which can be used to spread vines around the battlefield, charge forwards in a line (dealing damage and knocking creatures prone who fail their strength save), gain 5 hp and 5 temporary hp, or make a powerful melee attack which targets every single creature currently in the vines he spreads around.
• Noah, AI Warden: Sarissa Protocol
  • Noah has 6 legendary resistances, and begins combat with 2 points of Control.
  • These legendary resistances are represented by a loading bar on a computer monitor near Noah’s mainframe.
  • Noah gains points of Control from unspent legendary resistances, to a maximum of 8 points. These points can be spent on Noah’s turn to take actions on his statblock, without using Noah’s action.
  • Noah has no actions which directly cause damage, but it can use those actions to control security robots under its control, summon security robots, and take control of a party member who is a warforged.
  • Most of Noah’s actions cost Control to use; some even cost multiple points. Noah’s Anoikodomó Subroutine action is the only exception, which simply causes Noah to gain 2 points of Control and end its turn.
  • Noah’s mainframe and power core cannot be attacked until the generators powering its shield are destroyed. These generators all have their own HP, but share legendary resistances with Noah, meaning Noah can be forced to spend multiple legendary resistances in a single instance if multiple generators fail saving throws to an area of effect attack/spell.
• Saint Rasputin, Cult Leader: Chrysalis of Eternal Dawn
  • Rasputin has 100 legendary resistances which do not regenerate at the beginning of his turn. When Rasputin would be reduced to 0 HP, Rasputin can expend a legendary resistance to remain at 1 HP instead.
  • Rasputin’s resistances are represented as scars tallied on his bare chest, which fade when spent.
  • Rasputin must conduct a ritual tying another individual’s fate to his in order to regenerate a single legendary resistance. This person has the damage/effect transferred to them when the legendary resistance they are tied to is spent.
• Prototype Tarrasque: Unstable Iteration
  • The prototype tarrasque has 10 legendary resistances, which are represented by monitors on the walls of the testing facility showing the creature’s vitals.
  • The mad scientist who made the prototype is iterating on it during the fight, giving it random upgrades from a list. He asks the party for feedback during the creation process, and the party can vote to choose which of the two upgrades the prototype will receive next round. Each upgrade has a “risk factor” listed, which is a potential weakness that the prototype might gain when it gains the upgrade.
  • At the lair action each round beyond the first, the prototype tarrasque gains an upgrade, and a D10 is rolled. If the number rolled is lower than the number of unspent resistances the prototype has at the beginning of its next turn, the prototype gains the risk factor weakness for that upgrade (encouraging the party to not force the prototype to expend resistances).

[SECTION STILL IN PROGRESS. MORE BOSS MECHANICS COMING SOON.]