DELTARUNE: ASTRONOMY/The Gatekeepers/the ones that should be fought before fighting the secret bosses
Each one of them works differently, you have to fight some of em in order to get an item that trigger the secret boss fight in the chapter (while Chalkson, HER, FRIEND and Chucklezbub) some might just guards the said item or entrance (Watch-E, Jin-angshi and The Gravedigger).
Some of the gatekeepers' fights are inspired/based on other games, including:
Inspector Chalkson: Super Mario World
HER: Castlevania.
FRIEND: Dungeons and Dragons.
Chucklezbub: Pokemon.
As for those who don't fight, they basically uses specific gimmick in order to keep the players away.
Watch-E, for example, uses the Weeping Angels tactic, which when he been observed, he won't move, but if you took your eyes off him, he can travel from wherever he is to somewhere near you.
Jin-angshi uses frars to block the way, given her power as a yokai, and so, she uses surreal imagery to scare people away.
The Gravedigger doesn't try to stop the player directly, in fact, the player can ask him about the direction of the item, but here's the catch: don't trust the Gravedigger, as he'll give you the wrong direction, and once you you realised it, he's already changed the direction you'll take, putting you in an endless timeloop, where is just you, your party team, and The Gravedigger.
I.N.A (short for I'm not Alone) is basically uses puzzles, and by that, I mean putting people in a life-threatening situations and call it a "puzzle" and the player have to solve it in a certain amount of time.
All the Gatekeepers shares the freedom motif with the secret bosses, and if it's with only few notes.
I haven't thought of a better name for them, I think "Gamekeeper bosses" could fit them.