Just keep him away from your fish population, and you'll be fine.
Second basic alien, so basically same advice except he's a bit better at eating your tank than Sylvester. So be a bit more careful and always keep him in the corner opposite both side and corner of your fish (example: Fish: top right corner Balrog: bottom left corner).
He doesn't die from lasers - he dies from overeating. "G" stands for Gus and glutton and that is what he is. Keep him away from your fish at all costs unless dying has become good somehow. Never let him near your fish because usually he gets them in the end. Try to aviod using Star Potions, as despite dealing heavy damage, they cost $250, and the income from killing Gus is only $200, so it's only waste of money.
If Gus is cloned in Challenge Mode, he will start emptying everything in your tank. You must upgrade all your food quantities and upgrades for your disposal.
Although this Alien does not eat your fish, Destructor is still a pretty easy Alien to defeat. He is confined to the bottom where Rufus can get him easily, and just fires off missiles to kill your fish. Shooting the missiles blows them up and saves a fish. Not as hard as Gus, and sometimes not even Sylvester is as easy. Just keep shooting him, and when he fires his missiles, shoot them with your laser to blow them up. Destructor will always shoot his missiles after he finishes making his beeping noise (unless you paused it when he came in, in which case he would still make the noise while it's paused).
Psychosquid is a very dangerous alien if you are unprepared. When he first comes into your tank, shoot him away from your fish immediately. After a while he'll turn blue, drop his tentacles full of weapons, and will actually be healed if you shoot him now. If you shoot him in this state, a message will appear stating: "Stop shooting! Alien regains health!". So just wait until he changes back before hammering him again. He'll occasionally manage to get his healing form twice before he's killed, he's very annoying and hard for most players.
He is very dangerous during Challenge Mode when cloned in increased difficulties, because he will start emptying almost everything in the tank. You will need to have Presto, Gash, and Blip for your disposal.
Although he has a similar attack to Destructor, Ulysses fires two energy balls, but if you shoot these, they will become "live" and kill any fish (besides pets) that they hit. But, you can use this against him. When he fires his energy balls, shoot them in a way that they will bounce back and hit him.
He and Destructor are very dangerous in duplicating in Challenge Mode, because their troublesome deeds are when they shoot projectiles to kill fish. You will need to have Angie and Presto to revive all the dead fish.
It is a two headed snake of death. In order to destroy this Alien, you have to destroy both heads and get the one diamond without dying. Everything on him kills a fish: spines and heads will kill your fish. Keep him away from your fish at all costs! He takes a lot of skill and luck to beat but when you do kill him, you can enjoy the satisfaction of seeing his remains explode.
If cloned in Challenge Mode during increased difficulties, his clones will start emptying everything on your tank. Bring Gash and Presto for your disposal and upgrade your lasers.
See Tank 5-1 for more information.
One hard alien. He summons all the previous aliens at any given moment but one at a time. He also summons Mini-Sylvesters more commonly that can die in one hit but can eat a lot of pets before you see him. Shoot him until any other alien appears in which case kill that one first otherwise you risk total destruction. Just keep hammering him in between alien attacks and he'll eventually fall before you. Your prize? 5,000-25,000 shells depending on how many times you've done this. And on the first round one of the best pets ever: Presto!
In Sandbox mode, you can press Z, X, C, V, B, N , and M to summon an alien and kill it.
Alien Health Table
If you want to know how long will take to kill the alien, just use the table below. It shows how many clicks you will need to kill alien with particular wearpon. Feel free to add/change values if you find something wrong.
Note: These values are average. It might take more or less clicks for you to kill the alien. This was tested in Sandbox Mode.
!Alien !Laser lvl 0 !1 !2 !3 !4 !5 !6 !7 !8 !9 !Max |- |Sylvester |10 |7 |5 |4 |4 |3 |3 |3 |2 |2 |2 |- |Balrog |22 |15 |11 |9 |8 |7 |6 |5 |5 |4 |4 |- |Destructor |25 |19 |15 |13 |11 |9 |9 |8 |7 |7 |6 |- |Psychosquid |44 |29 |22 |18 |15 |11 |13 |11 |10 |10 |9 |- |Ulysses |37 |28 |22 |18 |16 |14 |13 |10 |10 |8 |8 |- |Bilaterus* |17 |13 |10 |9 |8 |7 |6 |5 |5 |5 |4 |} *for each head