I'm GMing Pathfinder 1e this weekend and my players will be delving through a cave that was once a silver dragon's lair. I want to have a bunch of encounters planned out so that I can stretch this crawl out to the end of session, since we have a guest player who we don't want in the story for too long or too short.

Stuff they will find so far:

-Group of Frost Giants in the entrance. They don't speak common, but are pretty chill guys if a player remembers to cast Tongues.

-SO MANY SPIDERS, while escaping down a spiraling cavern. I'll have them crawling out of the walls and stuff.

-A Black Pudding. Never used one of these, and I don't think my players would know what to do immediately.

-Long underwater cave with some aberrations in it, maybe gibbering mouthers. Also a gigas clam with a huge pearl to lure in the party ninja.

-Big ending surprise - it's not a silver dragon's lair, it's a black dragon's lair, and this whole plot was him luring you to get eaten. Why is this cave so long? Because the black dragon just uses his underwater secret entrance/exit for his schemes.

Party is level 10 and there will be 5 of them, 6 with animal companion. Does anybody know any good encounters for a group like this? Doesn't need to be system specific - I'd love ideas for cool cave traps and stuff.