Banishment if the creature isn't on its native plane and lacks planar travel. Maintain concentration for a minute and it's gone for good, no further saves.5e has auto win spells? Most of them let you save on consecutive rounds and there are no more save or die. What spells are you talking about specifically? Hold Monster is one where they lose a round of actions or more. I what else?
From an active perspective, I like how Dragonbane has big monsters pull multiple initiative cards. I can easily see a solo in D&D getting 3 actions at 3 different initiatives (eliminate multiattack and fold lair actions into this). From a strategic and reactive use of things like Legendary Resistance, maybe it has to give up a forthcoming action to do it?The intent is to keep the action going and prevent it from being one-sided. It should feel like an ebb and flow where both sides are grinding each other down and the PCs can’t overwhelm the bad guy - instead they have some sort Of trick or ability that allows them to keep menacing the party.
I would like to see it moved from an automatic ability the PCs know they have to burn through to a more strategic choice or effect that the DM can manipulate the timing of for dramatic effect or that the PCs might be able to goad or accidentally activate and be surprised by it.
Sort of, but that's unlikely to be the case if it's the BBEG of a story or adventure. Unless the DM's off their game, getting that Banishment off is probably going to be the story point instead of the story killer.Banishment if the creature isn't on its native plane and lacks planar travel. Maintain concentration for a minute and it's gone for good, no further saves.
Sure, but Legendary isn't just for BBEGs, it can be for any tough fight against a lone opponent.Sort of, but that's unlikely to be the case if it's the BBEG of a story or adventure. Unless the DM's off their game, getting that Banishment off is probably going to be the story point instead of the story killer.
Right, I think it is important to remember than not every "solo" is also a "boss" -- and I do think that bosses need different or additional kinds of abilities to fullfill that role. But a big solo monster just needs to not be a boring pile of HP and claw attacks to get smashed by the party before its second initiative. Action economy is king in 5E.Sure, but Legendary isn't just for BBEGs, it can be for any tough fight against a lone opponent.
Hypnotic Pattern is very powerful for sure yet still not “auto-win”. In the case of a boss with minions, I would think one of the unaffected minions would spend their turn to move and then shake their boss out of the stupor.Hypnotic Pattern is a big one. It could, for example, put the boss completely out of commission while the PCs deal with the minions, no matter how long it takes, and then they all focus-fire the boss.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.