Two moves, Optional 3rd.

Destructo Disc and special beam cannon after you see their HP take damage from the hit from the disc. It's a small stun animation that leaves you with a long enough window of time to hit them with special beam cannon. For how much ki it cost to use the cannon vs the damage output makes it so worth it. Also both moves can not be guarded. First two teachers you need to go to are krillin for Destructo Disc, and piccolo for special beam cannon. You can chain outher mover to hit with Destructo Disc. Side note use (innocence cannon) taught by Buu. If you are at the top of any map and hit your opponent with it you can charge your ki as they fly away stuck in a ball. Also if you time it right you can hit them with a Destructo Disc as they hit the ground, after the disc hits you can special beam cannon.
Timing is important here, but those three moves in a beam users arsenal are very powerful.

Hope you enjoy my advice.

If this helped then I am glad I made this guide.
Android 18's move Deadly Dance is a good melee spam move that you can chain for good combos. Or spam it with all your Ki and watch their HP drain. Keep in mind it also repels weak ki blast.