Very tight strat and probably reserved for top players/checkpoint runs. When climbing up to the platform, stay low to the ground and downright dash.
Hold grab, dashjump on the cue to get the most speed from the ultra (make sure to hold it to not get a hyper), and immediately buffer two jump inputs.
Buffer a downright dash when entering the next room and bhop.
Once you glide or get stopped for a frame, downright again and bhop to get under the bubble in the next room.
These three bhops are all feel and take a very long time to get consistent.