Sinistar Tips:
1. Fire into asteroids to shake loose "Sinibombs". Collect all 20. You'll need at least 13 to kill him (he has 13 pieces) and probably a few more for ones that hit something else first ("Sinibomb Intercepted" notification).
2. The joystick features progressive speed--push it partway and you'll go slower so you can collect those SB's more easily.
3. The Warrior ships are murder but mostly they stop firing at you when you stop firing. When you're surrounded, stop firing much and run in erratic patterns and circles. Get outta there!
4. Make sure Sinistar is NOT on your radar screen--move away. On the SECOND statement that he makes after he's complete and alive, unload 13 Sinibombs as fast as you can (trill the fire button). They will home in on him. Then start collecting more--your goal is to head into the next level with at LEAST seven Sinibombs in your rack. If one or two Sinibombs got intercepted, wait til you're close to him before you fire them or they too will probably get intercepted.
5. You will be really busy on the Warrior Zone and find slim pickings for asteroids on the Void Zone. Use the radar screen to locate asteroids in the Void Zone. But if you didn't do Step 4, you're probably gonna die.
6. If you can't find enough asteroids to fire into to shake Sinibombs loose, get close to Sinistar (find him on the radar screen) and steal the Sinibombs that the Worker ships are bringing to make Sinistar.