I have my PCs entering a mansion owned my an illusionist-rogue type of BBEG. He's going to be casting Minor Illusions, as well as Hallucinatory Terrain throughout the mansion to mislead players into falling for traps, walking into unfavorable scenarios, as well as getting the jump on them.
How do I implement this as the DM, without making it entirely unfair to the players? The spell Hallucinatory Terrain reads as such:
If the difference isn't obvious by touch, a creature can attempt to make an Intelligence (Investigation) check against your spell save DC to disbelieve it.
With that said, if the players walk into a room, and see a finely placed dinner table, chairs, and smell and see the fresh meal placed before them (as an illusion), at what point do they realize it is all fake, and that they're truly standing on a giant trap door?