Before you can enter mission 4, you must complete missions 1-3 (unless automatically advancing from mission 3).
- For mission 1 you start with:
- Full flamethrower fuel.
- 12 missiles.
- No other weapons
- no credits.
- For other missions, you start with:
- Full flamethrower fuel
- No special weapons.
- If automatically advancing from previous mission, whatever credits you had, otherwise no credits.
What isn't carried between levels.
- Health (resets to full)
- Flamethrower fuel (resets to full)
- Partial magazine ammo count (resets to full)
The last one is very abusable: Three weapons, Missiles, Thermo Grenades and Photon Blasters have magazines. Resetting magazine ammo count means partial magazine becomes full. With Missiles and Thermo Grenades, this can cause up to 5 shots to appear out of thin air (10 for Photon Blasters).
What heals you
- Exiting level (to full health)
- Rescuing any hostage (to full health)
- Eating any food item (restores 25% of your health).
Boss levels are special. All your special weapons are taken away, and flamethrower fuel becomes infinite.
If you are brushing against the ceiling, your vertical speed increases (unless it is already at maximum) even if you don't actually move vertically. Thus it might be advantageous to actually brush ceilings.
If you brush against ceiling sloping down, you can't move forward.
Walls have one-way zones (and those zones are pretty wide). These zones can't be entered from direction normal to wall, but can be entered from direction tangent to wall.
Left+Right when flying freezes your horizontal motion. Quite useful.
Spikes only hurt you while they are coming up. Fully up spikes don't. But beware, the spike coming up animation is longer than it looks.
Mother Alien collision bug
When Mother Alien (mission 1 boss) is firing, collisions against harry are not checked. The window is just big enough to phase through the boss left to right without taking damage.
Similar thing (albeit with much wider time window) is with Sentry Droid THX-1138 (mission 3 boss) when the droid is executing the "jump press" attack.
Also, when Alien Leader (Mission 4 boss) is swinging its microphone, the hitbox is just the microphone (albeit it does 75% damage in one hit).
Boss OMEGA glitch:
This is useless, because you can't get OMEGA to boss zone, nor can get OMEGA from there. Using OMEGA against boss instantly brings it down to 0HP, but does not kill it. Flamethrower will then bring health down to negative values (boss dies when HP reaches -12).
Boss explosion damage:
Another useless trick. It turns out explosive weapons that can hit boss (Micro-Nuke and Thermo Grenades for missions 1, 3 and 4) deals severe damage to the boss (over 50% of health of any boss hit).
Speeds (turbo play on)
- Normal running: 16 pixels / frame
- Running in forward current / conveyor: 24 pixels / frame.
- Running in backward current / conveyor: 8 pixels / frame.
- Flying (full speed, independently for both axis): 10 pixels / frame.
This weapon is pathetic. The only good sides are that ammo is free and you start with it. Avoid if at all possible.
- Dispenser: F
- Unit price: free / full fuel
This weapon is way more useful than flamethrower, but still pretty useless, because you can't hit enemies when running (and additionally shots have tendency to go to wrong places).
These can be used to destroy alien generators in one hit. They don't explode in contact, but if one explodes near enough, it will take out the generator.
- Dispenser: G
- Unit price: 15 credits / 6 Grenades.
This is useful weapon. Unfortunately, not all enemies can be hit without slowing down. Damage output is higher than flamethrower and range is much greater.
- Dispenser: P
- Unit price: 15 credits / 11 shots.
The most useful weapon for TAS. Unfortunately, these have tendency to fire unlocked (can sometimes be exploited) or lock into completely wrong targets. They also have tendency to fail to reach target before you do.
This weapon doesn't target and don't explode on contact with explosive barrels (and neither would it work against bosses).
- Dispenser: M
- Unit price: 20 credits / 6 missiles.
Dropped bomb that explodes after some time, doing severe damage to nearby stuff. Expensive price and the detonation timeout make this pretty useless weapon. Pretty much only thing it is good for is blowing Alien Generators (and even for that, Themo Grenades are better).
- Dispenser: N
- Unit price: 20 credits / nuke
Destroys all enemies on screen in one instant flash. Expensive, but very powerful.
- Dispenser: O
- Unit price: 20 credits / unit