I'm creating a CR21 boss for my medium-level party of six players to fight. I know that action economy is a big disadvantage for a single enemy fighting an entire party, so I'm giving the boss the ability to attack 4 times per turn (20-35 damage per most attacks).

I know the most common way to give a creature multiple attacks is to give it Multiattack, an action that allows it to use its attack abilities several times in one go. I'm considering instead rolling initiative for the boss 4 times and giving it a whole turn for each initiative value, giving it 4 separate attacks.

Will this have a significantly different effect on the battle than giving the boss a standard multiattack?

A couple thoughts I've had:

• This allows the boss to use more bonus actions per round. The boss I'm designing doesn't have any nonstandard bonus actions, so I don't think this will make a big difference.


• This allows the boss to move more often. I've divided the speed I want the boss to have by the number of turns it gets per round, so its total movement per round will be the same.


• This gives the boss more reactions. I can see this making it quite a but more difficult. I'm not planning on using many reactions when I play the boss, though.

The D&D 5E system already has built-in rules for important creatures acting out of turn: Legendary Actions and Lair Actions.

Legendary Actions happen a certain number of times each turn (usually three), though some specific instances take up more than one. These actions take place after another creatures turn, interrupting the initiative order. They range from casting a spell, making attacks, using an ability, extra movement that doesn't provoke attacks of opportunity, to more exotic things.

Lair Actions are similar, but take the form special things the creature can do with the environment (or the environment does to the creature's benefit). They always take place on Initiative Count 20.

If your players know the game (experience with other DMs, or being DMs themselves), they should be comfortable with the concept. Adding your own house rules when there are already mechanics designed in the game just tends to add confusion.

Legendary Actions are the standard way that monsters are given to act at multiple points in the round. These can be in the form of special attacks, spells, or whatever other sorts of actions you like.

You've addressed most of the objections to using whole turns in your updated question.

Numerous spells, abilities, and actions change

In addition to the differences you have mentioned, the boss...

• Is less affected by one good or bad initiative roll.


• Can try to save four times per round against hold monster and similar save-or-suck spells. Other effects, like a monk's Stunning Strike, are unaffected.


• Is forced to save four times per round or take damage from spirit guardians and similar damage spells.


• Is much more quickly affected by save-X-times-or-suck spells, like contagion and flesh to stone.


• Can grapple or shove four times per round. (One cannot substitute a grapple for an attack within Multiattack, unlike Extra Attack.)


• Can stand up from prone four times per round.

Legendary Actions are the normal answer

As the other answers stated, Legendary Actions avoid all of these problems by allowing a Legendary creature to act outside of its own turn. An Adult Red Dragon is one such Legendary creature and has the following Legendary Actions:

Legendary Actions

Can take 3 Legendary Actions, choosing from the options below. Only one legendary action can be used at a time, and only at the end of another creature's turn. Spent legendary actions are regained at the start of each turn.

Detect: The dragon makes a Wisdom (Perception) check.

Tail Attack: The dragon makes a tail Attack.

Wing Attack (Costs 2 Actions): The dragon beats its wings. Each creature within 10 ft. of the dragon must succeed on a DC 22 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Legendary Actions can be anything. A high-level Legendary spellcaster could fire off four spells per round. A Legendary demon lord could teleport around the battlefield, striking PCs who thought they were safe. A Legendary archdruid could rapidly switch between different beasts, each one making a different attack.

One more thing - if you don't want your boss to fall to the first spell that the control wizard casts, don't forget to add Legendary Resistances. They may feel cheap when you use them, but allowing the boss to auto-save a couple of times helps the encounter be memorable in the right way. Turn 1 banishment against a creature with 8 CHA shouldn't be the answer to everything...