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[edit] General strategy

1. Get a big gun.
2. Run about.
3. When you see something that moves, jump and shoot.

[edit] Specific strategies

Rocket Launcher

As you run around, start charging up the rocket launcher. Then when you see something move, jump and unleash 3–5 rockets into them. You barely need to aim. Works best on smaller maps.

Shock Rifle

Fire off a shock ball (secondary fire), then hit the shock ball with a normal shock rifle beam (primary fire). The shock ball will explode into a big glowing ball of death. Useful if someone is hiding behind a corner.