Legendary Enemies

[Nagog]

Goooooood Morning Playground! I have a lovely discussion topic for ya'll today that I'd love to have some input on: Legendary enemies!
In your opinion, what is the best/most engaging Legendary Enemy to play as a DM, best for your players to fight, and favorite to have in a campaign? I imagine Legendary Enemies to be along the same lines as a Kraken, the Terrasque, or a Dracolich, but anything big, bad, and fun will do!

[Nagog]

Personally I enjoy the Kraken, both as a player and as a DM. The unique environment of a ship/under water makes for a memorable and difficult battle, and as a DM not having to worry about Legendary Saves in favor of having really great bonuses (even a Diviner would have trouble making a Kraken fail a save) is a wonderful and straight-forward fight compared to many other legendary creatures that have mechanics that are highly debated, like how LR translates into the story, etc.

[darknite]

I like Liches a lot. They are multi-dimensional, intelligent and slippery. This means they can show up in just about any kind of campaign, in any terrain and with any kind of support. They can lead armies, be shadowy manipulators, rock the foundations of reality or whatever. You can count on them to have a ton of contingencies and provide solid opposition to your players. And forget killing one, unless you as the DM decide to provide a path to discovering their phylactry.

[Vorenus]

My favorite Legendary enemies are those with high intelligence. I dislike Legendary enemies that can't think tactically. Liches are excellent Legendary enemies. One of the reasons they are excellent Legendary enemies is because they are intelligent. They can make plans, they can think tactically, they can be flexible and adapt if necessary.

[Vorenus]

I forgot to add: My all-time favorite Legendary enemies are former player characters who have turned to evil. Whenever I get a chance to do that, it's always very rewarding for the players when they encounter an enemy boss that used to be a PC either in a previous campaign or in the same campaign. I always talk to the player whose PC it used to be to make sure they like the idea, and I've never had a player dislike the idea. My favorite example of this was a slow-burn in a completely different RPG system. In that game, I talked to one of my players about slowly becoming possessed by a demon and developing new demonic powers over time, with the long-term goal that the character would eventually be fully possessed and would no longer be a PC but would become an NPC. It worked beautifully. The other players never saw it coming. The big reveal when the possessed character became a full demon host and ripped apart another PC was shocking to everyone. The survivors managed to drive the demon away, but they didn't kill it. Years later in a different campaign with the same players, now playing entirely different characters, they started pulling on plot threads that ultimately led back to the former-PC who by this point was a powerful demonic magic-user. When the players realized who they were facing they went crazy with excitement. Of course, their characters didn't have the connection with the former PC, but the players did and it was great. It takes a lot of work to build up to something like that, and you have to be really patient, but the payoff is huge.