Table Top RPGs and Videogames concepts doesn't always mesh up nicely.
While it seems awesome to have a very specific way to kill a boss, it usually detracts from one of the best trumps of Tabletop RPGS over MMOs and such - no scripted events.
Boss mechanics were something that were cooked up to give players of a way more limited type of media - a videogame, with a finite set of actions possible - something especially interesting on the end of each level, dungeon or raid.
The way games deal with this varies a lot. Some won't tell the player what to do and leave him or her to die over and over until they figure out what to do - Like most Megaman games. Other games will warn you about how you should behave and even will give you in-game hints about what to do - like recent WoW raids and dungeons.
However, boss scripting and mechanics is something you need for the media to work, if you want to have an interesting boss fight. You need to program in advance what the players can do and how the boss will react to the things they do since you won't be there playing the boss against them, like most DM's out there can.
In games, death is cheap - it's not really a big deal if you die or, if it is, you can probably wiki your way out of the problem with a well placed pause and some quick googling. That isn't true for Tabletop RPGs (well, at least not for most of them). Death in those is, more often than not, a really big deal. Sending your players to a death puzzle in the form of "solve or die" isn't nice unless you game is some sort of Saw-based thriller or some old school Gygaxian masochist fest. While those are attractive to some hardcore players, that isn't true for everyone.
Anyways, to the point. The idea of secret boss mechanics, while attractive on videogames, doesn't really translate well to a tabletop rpg. On a TTRPG, death isn't cheap - it hurts, both your character and your player's emotions. Even if you agreed that characters dying is a very real part of your game beforehand, dying for a puzzle fight gives the player the feeling of being cheated. They won't feel they had enough time to solve the puzzle, and they will complain that it wasn't clear enough. For most players, dying for something like this is just 'unfun', so it's something you should try to avoid.
More so, having a single point of success is a somewhat difficult and unfair thing to do on a TTRPG. When you create some abstract rule like "the lich can be only damaged by the bones of the skeletons he summons", you are invalidating all of your party's choices. You're forcing them to ignore their character sheets in favor of some arbitrary rule. Things that they put time and effort to get and to customize - their special weapons, their spells, etc, won't be worth anything on this setting. The better thing to do is to make the boss encounter solvable in different, coherent and logical ways. Use what the party has to offer and create ways for everyone to contribute doing what their characters can do best, so everyone can shine and have a good time.
Be ready to change your boss mechanics on the fly to adapt to whatever the group throws at you, and be prepared to let your boss die if the players manage to pull of something that would work but you didn't foresee they would do that. Projared's Ballista Bat tale is a good example of a player circumventing the DM's expectation, and a nice video to watch if you have some spare time. On the video, one of Projared's players uses a Warcraft 2 Balista shot as a club to clear the way to the big bad, avoiding several encounters the DM had set up. When the group went to confront it, the player in question smashed the gigantic balista shot on the Evil Overlord and pinned him down with it, basically solving the encounter in one single attack instead of the planned battle. The video serves as a good example of a planned game session taking a left turn and going into unplanned territory — and the DM rolling with it instead of forcing the players to stick to his or her plan.
Keep in mind that designing a boss fight for a TTRPG is not something you should do to be frustrating. You should aim to entertain your players, to give them fun. Don't ever let some idea of a "cool hidden boss mechanic" hamper your game. Make the boss battle epic by making the villain, and most importantly, the players, do epic stuff on epic places.
Even a regular sword-fight without secret mechanics would be awesome if it took place on moving platforms inside an active volcano that also happens to be full of young, red drakes that are looking for a meal.
Make your encounters epic by telling an epic story, not by hiding mechanics from your players and hoping them to read your mind. Abuse the power of the TTRPG and do all the nice things that most videogame developers can only dream of doing on their games.
Never forget that you're the Game Master. You should never be enslaved by preconceptions about how the boss fight should be played - feel free to change everything if you need to make everything more fun for you, and for your players.