There have been a lot of complaints and discussion about Legendary monsters, particularly the Legendary Resistance trait. The existence of Legendary Resistance should not be seen as a slap to the face of spellcasters everywhere. Instead, it should be taken as a strong hint from the designers that perhaps the spellcaster's talents are better used elsewhere on the battlefield. It is the DM's job to design the encounter so that that is possible.
That means that the so-called "problem" is less in the monster design and more in the encounter design. A lot of DMs seem to think "Legendary" means "solo," even though there is no such indication in the rules. I'm sure 4e is largely to blame for this misconception, but I'm willing to bet people who never played 4e are falling into the same trap.
In a properly designed Legendary encounter, there should be teeming hordes of minions leaping to the defense of the BBEG. If there are not, and if the BBEG is stupid enough to stand and fight without them, the DM is to blame for the imbalance, not the rules. No Legendary creature should be stupid enough to fight alone.
In a properly designed Legendary encounter, different classes have different roles, and those roles are magnified due to the increased danger level. I think many people are unclear on what those roles actually are, so I'll offer my take on them:
-- Most arcane casters are better at widespread damage against less-resistant targets. They have no business going after the BBEG. Their job is to take out the trash before the trash takes out the martials. Arcanes who are not built for damage are probably built for control, but their role is the same -- keep the minions out of the martials' hair. (Fireball and meteor swarm are great spells, but it is stupid and wasteful to cast them at a single target.)
-- Characters with strong healing magic should obviously use it when necessary. Otherwise, they should focus on buffing the party, debuffing the trash, or general support. They might use physical attacks against the BBEG, but only if they can do so safely, and only if there's nothing better to do. They should not attempt to control or debuff the BBEG, any more than the arcane casters should.
-- Druids, in particular, are less likely to fit neatly into any of these categories. They should do whatever the individual druid is built to do, but watch the flow of battle and be prepared to shift roles as needed.
The Solo Problem
If you want to have solo encounters in 5e, there's nothing wrong with that, but I would not use Legendary creatures to accomplish it. The Monster Manual doesn't really have anything suitable, so it might be a good idea to come up with something else.
We need to come up with a good template or catalog of traits that can be given to a monster to make it a viable solo. Of the top of my head, this would include:
-- More hit points. I would welcome suggestions for some kind of formula. I feel like it's not as simple as a flat multiplier. Should the monster's AC be included in the calculation?
-- Something like Legendary actions. In many cases, existing Legendary actions are exactly the best fit, which is one reason so many people make the mistake of treating "Legendary" as "solo." But it might be wise to create a list, weeding out existing Legendary actions that are not appropriate for a solo monster. We also need some solid guidelines for the action budget -- probably broken into tiers.
-- The most pressing need is a way to deal with "save or suck" that is not as harsh as Legendary Resistance. I have seen a few suggestions, but I'd like to see more. One option would be to give solo monsters higher saving throw bonuses across the board. This is a rather swingy way to deal with it, allowing the spellcaster to attempt to cut the fight short, but with a greatly reduced chance (but not zero) chance of success. Another option is something like Legedary Resistance that only kicks in on "second round" saving throws -- it lets the spell take effect the first round, but then the monster can automatically break free on its next turn. What are some other good options?
Perhaps a system where different body parts are treated as separate entities (kind of like a hydra)? So if you cast hold monster on a dragon's wing, it can no longer fly or make wing attacks, but the rest of its body is still going strong? This probably wouldn't work for every monster, but it might be a useful tool to have in the kit.
That means that the so-called "problem" is less in the monster design and more in the encounter design. A lot of DMs seem to think "Legendary" means "solo," even though there is no such indication in the rules. I'm sure 4e is largely to blame for this misconception, but I'm willing to bet people who never played 4e are falling into the same trap.
In a properly designed Legendary encounter, there should be teeming hordes of minions leaping to the defense of the BBEG. If there are not, and if the BBEG is stupid enough to stand and fight without them, the DM is to blame for the imbalance, not the rules. No Legendary creature should be stupid enough to fight alone.
In a properly designed Legendary encounter, different classes have different roles, and those roles are magnified due to the increased danger level. I think many people are unclear on what those roles actually are, so I'll offer my take on them:
-- Martial classes excel at single-target damage, especially against the Legendary creature itself. Their job is to attack the BBEG.
-- Most arcane casters are better at widespread damage against less-resistant targets. They have no business going after the BBEG. Their job is to take out the trash before the trash takes out the martials. Arcanes who are not built for damage are probably built for control, but their role is the same -- keep the minions out of the martials' hair. (Fireball and meteor swarm are great spells, but it is stupid and wasteful to cast them at a single target.)
-- Characters with strong healing magic should obviously use it when necessary. Otherwise, they should focus on buffing the party, debuffing the trash, or general support. They might use physical attacks against the BBEG, but only if they can do so safely, and only if there's nothing better to do. They should not attempt to control or debuff the BBEG, any more than the arcane casters should.
-- Druids, in particular, are less likely to fit neatly into any of these categories. They should do whatever the individual druid is built to do, but watch the flow of battle and be prepared to shift roles as needed.
The Solo Problem
If you want to have solo encounters in 5e, there's nothing wrong with that, but I would not use Legendary creatures to accomplish it. The Monster Manual doesn't really have anything suitable, so it might be a good idea to come up with something else.
We need to come up with a good template or catalog of traits that can be given to a monster to make it a viable solo. Of the top of my head, this would include:
-- More hit points. I would welcome suggestions for some kind of formula. I feel like it's not as simple as a flat multiplier. Should the monster's AC be included in the calculation?
-- Something like Legendary actions. In many cases, existing Legendary actions are exactly the best fit, which is one reason so many people make the mistake of treating "Legendary" as "solo." But it might be wise to create a list, weeding out existing Legendary actions that are not appropriate for a solo monster. We also need some solid guidelines for the action budget -- probably broken into tiers.
-- The most pressing need is a way to deal with "save or suck" that is not as harsh as Legendary Resistance. I have seen a few suggestions, but I'd like to see more. One option would be to give solo monsters higher saving throw bonuses across the board. This is a rather swingy way to deal with it, allowing the spellcaster to attempt to cut the fight short, but with a greatly reduced chance (but not zero) chance of success. Another option is something like Legedary Resistance that only kicks in on "second round" saving throws -- it lets the spell take effect the first round, but then the monster can automatically break free on its next turn. What are some other good options?
Perhaps a system where different body parts are treated as separate entities (kind of like a hydra)? So if you cast hold monster on a dragon's wing, it can no longer fly or make wing attacks, but the rest of its body is still going strong? This probably wouldn't work for every monster, but it might be a useful tool to have in the kit.