Cloaking can only be obtained if you are in a Shark or Spider. Cloaking allows your ship to be invisible on the attack screen. If used in conjunction with stealth, your ship will become completely invisible to any opponent who doesn’t have X-Radar on. If you are hidden on screen, it makes it quite easy to sneak up and attack unprepared enemies. Cloaking does take energy, which slows your recharge rate, so be mindful of your energy status whenever you are cloaked.
Cloak is the only item that will make you invisible to the naked eye. Any enemy not using xradar won't see you on their screen. If you do not use stealth simultaneously, then enemies WILL be able to see you on their radar, warning them of your presence. Turn both stealth and cloak on to become entirely invisible. Cloak and stealth will drain alot of energy. Cloak itself will automatically turn itself off when you fire any weapon, except for portals and rockets. It will only be available to very few ships. Some of them will have it enabled by default, and therefor cannot lose it due to damage. Other ships will have to collect greens to get the cloaking device.
The cloaking device is one of the most potent weapons in the game. In combination with stealth, you can turn your ship into an invisible killer that will pound an enemy with your L3 bullets as you decloak, severely damaging / killing him while you cloak again, turning around for another strike. The element of surprise is usually enough to ensure a kill, or at least to damage him in a way that thor or bomb is enough to kill him. Timing is very important here, because he should not be able to dive behind a corner, or hide in a nearby safezone. Usually, your first attack is the one with the best chance of killing him. Sometimes it is wise to run away after a failed attack on someone, because he / she will try to retaliate. Find a new target instead, one that is not yet aware of your presence.
Pursue your target, fly right behind him matching his speed and vector, and release a volley of bullets. If he doesn't die, simply cloak again and fly away a bit. Turn off your cloak and stealth when you're at a safe distance, recharge, and attack again. Your opponent will be aware of your presence now. If he has xradar, he will have switched it on. If he doesn't he might have dropped a portal to escape to when things get hot again. Turn on antiwarp to deny him the ability to use his portal, and charge again until he dies.
When you are running away from someone that has xradar turned on, ALWAYS turn off cloak. It drains alot of energy, which you need to get away from him. If posible, leave on your stealth device. This way, the enemy chasing you will have to keep his xradar on. He will have less energy to spare, meaning that less bombs and bullets will be coming your way.
And.... when you are not a cloaker yourself, remember to check xradar every now and then. It is quite humiliating to be killed by a spider like that. If you want to kill any spiders that try to kill you, simply fly around (xradar on) and watch any cloakers attempting to attack you. They will try to get right behind you, so drop a portal when one is close. Warp when he passes the portal, and nail him with your guns. Ofcourse, you shouldn't make any weird moves before that, since that will alert the cloaker that you know that he's there. He will then be more careful, and thus harder to kill.
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When you activate the cloaking device your ship becomes INVISIBLE, however your radar image can still be seen. Cloak is an enormous drain on recharge rate and turns off when you fire. Note: A ship that is stealthed AND cloaked is completely invisible on RADAR and on the visible screen area to other ships that do not have XRADAR turned on.
As you should know by now, cloaking is an ability that can only be acquired by the Spider [or Shark]; in the right hands it can be a very effective and very annoying tool. Activated, it renders you invisible to others on the screen, but unless you have stealth on as well, you will still appear on the radar map. It is amusing to approach an enemy cloaked but not stealthed; he will spin around at first, confused, and will sometimes hurt himself trying to hit you with a bomb. With both cloak and stealth activated, you are completely undetectable, but suffer from a double charge rate decrease. Realize that an enemy with x-radar on can see through both cloak and stealth, so watch him closely to see if he knows you are there. Sometimes, however, an enemy will pretend not to see you and will try to fool you into following him into a trap.
The instant you fire a bomb or a bullet, your cloaking is deactivated, and must be turned back on again by hand. A common tactic is to approach your victim cloak, fire a quick bomb, recloak and approach from another angle and fire and repeat.