I think the only new attacks will be the ones stated in the outline, Ginyu's and 18's attacks, and perhaps a few more for the other character's higher transformations...like Vanishing Ball for Kid Buu. Then again, I'm almost positive Vanishing ball is just Buu's version of Death Ball. Then again..again...Buu has the ability to gain attacks from other characers now...so maybe death ball will be available for buu to gain in place of adding vanishing ball.
On that note, If Buu can absorb attacks from characters, I think it should go like this...
Gohan - Powerbeam (Has Kamehameha but so do 3 others)
Goku - Kamehameha (Painfully obvious)
Krillin - Scatter Beam (Kind of interesting and would be worth hunting down a Krillin)
Piccolo - Special Beam Cannon (Painfully obvious)
Cell - Kamehameha/Gallit Gun (no other choice really...unless you want SBC instead)
Vegeta - Gallit Gun (obvious)
Frieza - Finger Laser (A pretty good choice. I dont think anyone really wants Buu lobbing death balls around so Finger Laser works best)
Trunks - Burning Attack (not much choice here)
Buu - Nothing
this way, attacks are mixed so Buu wont get Kamehameha from everyone who has it (Gohan, Krillin, Cell, Goku). This will add some Variety so if the player wants a specific attack, that player will have to do some hunting rather than say "I want Kamehameha, so I'll find the nearest Gohan, Goku, Cell, or krillin!" Or perhaps Gallit Gun with Vegeta and Cell form 2...or Special Beam Cannon with Piccolo and Cell.
Because Cell's attacks are just copies of other's attacks, I just think Kamehameha/Gallit Gun would be better than SBC and since Cell stays transformed if he dies, it gives a bit of variety for what attack you get depending on if Cell is transformed or not.
Then again, you could make it so you get a random attack from the player's arsenal...such as when you absorb goku, you have a chance at getting Kamehameha, Spirit Bomb, solar flare, or Kame Torpedo. just an idea.