Where are the castle 30 secret stars on super Mario 64 ds?

You're asking about a tricky one! There's no "Castle 30" in Super Mario 64 DS. The game has eight main courses, each with their own set of stars, and a final "Castle" level.

The 30 secret stars are distributed across these courses:

* Course 1: Bob-omb Battlefield: 8 Stars

* Course 2: Whomp's Fortress: 8 Stars

* Course 3: Jolly Roger Bay: 8 Stars

* Course 4: Lethal Lava Land: 8 Stars

* Course 5: Shifting Sand Land: 8 Stars

* Course 6: Snowman's Land: 8 Stars

* Course 7: Tiny-Huge Island: 8 Stars

* Course 8: Rainbow Ride: 8 Stars

It's likely you are thinking of a "Castle" level that is in the game's final "endgame" sequence. These levels do contain more Stars.

If you're looking for the locations of all the stars, including the ones you get after beating the game, I can help you find detailed guides and walkthroughs for each level. Just let me know which course you're interested in, or if you're looking for the "endgame" level stars!