Possibly unique deep dark portal boss fight idea

Instead of just a typical boss, it would be more unique if the deep dark dimension portal, once activated by specific sound combinations, spawns a related boss and this boss either 1=has to be defeated before being able to enter the portal (as it is so powerful it instantly kills those that try before it’s defeated) or 2=can only be defeated using something obtained after having entered the portal’s dimension so it requires becoming more powerful from the dimension to actually defeat. (Like the warden, it would be a unique mob in either of these ways as it either is 1=only needed to defeat as the main obstacle to enter the portal and doesn’t drop any item or 2=its something not intended to be immediately faced (similar to the warden that incentivises stealth strategies and thus establishes another link to them) It could be essentially tied to just the ancient cities to manage the choice of whether to face it better rather than roam free like withers or could be a mix like the ender dragon or even be limited to spawning and only existing in low light levels which incentivises keeping the light levels low for this encounter