Enemies: 6x Bomber Helis and 4 respawning Robots
Attack the helis with any weapon except the soundwave, black hole generator, or atom bomb, as these should be kept for the final levels. However, use them if you get into trouble.
To dodge the bomb attack, hyperjump and use time break and you should not take any damage, after you dodge it, follow the helicopter and shoot it while it bombs the ground. If the helis are not using the bomb attack, you can usually just run from right to left without taking any damage.
Either use the same tactic in the zones 2-1, 2-2 and 2-3 (Bomber Helis need 6 grenades to be taken down) or use the ammo you've acquired for miscellaneous weapons. Try not to use the ammo for better weapons. It's not necessary to waste your time taking them down with the pistol, knife, or bow. If you happen to get ammo for the following, just make sure to use it efficiently (shotgun blasts should be used in close proximity to avoid wasting bullets on the edge of the spread):
- Shotgun
- Double Shotgun
- Machinegun (you should have plenty of machinegun ammo right now so using a little bit won't hurt)