Like other prototype defenses, it will only last for a limited duration after being deployed.
The Flotsam Cannon is a defensive cannon that deals high damage per second with a small splash radius. When it is destroyed, after a short delay, it will explode, causing massive damage to everything in an area. This includes both troops and buildings. It will also trigger Mines, Boom Mines, and Shock Mines.
The area of effect is visible after the building is destroyed. It is represented with a circle with a skull image inside it.
The Flotsam Cannon has a small blind spot where it cannot fire upon, similar to that of a Machine Gun.
If one is seen, try not to clump up your troops. Like the S.I.M.O., it deals high damage and fires very fast, but it also deals splash damage, which is dangerous to many units.
Never ever use melee units such as Warriors against this defense, because when they destroy it, any buildings left nearby will stall them and thus allowing all of them to be blown up. To counter this, time a Flare correctly so it takes place right after the Flotsam Cannon is destroyed.
A Flare can move troops to safety if the bomb is about to explode, but you need to anticipate the explosion (for example, by damaging it with Gunboat Weaponry just before it runs out of health) or be very quick. However, this can drastically change your attack if the troops are very spread out, as the Flare will regroup all your troops.
Dr. Kavan's Ice Shields ability can protect troops from the deadly blast. Use it just before it explodes to minimize casualties.
Since Remote Hack can capture prototype defenses, if the Flotsam Cannon is hacked and other buildings destroy it, anything in the close proximity would be put at risk.
Do not place it nearby critical defensive buildings or the Headquarters, because the explosion harms your own buildings. It will also detonate mines, so it is not a good idea to place many around it.
At Mark I, the Flotsam Cannon resembles a rather large sea mine, with seaweed both on it and around it, as well as a single starfish. Dynamite fuses are installed all around itself, and there's a circular rail in the middle, assisting the porthole in rotating and firing at enemies. It's painted in a bronze scheme.
At Mark II, it now has a metallic casing. The seaweed on it is removed. Rings around the fuses and a circular platform to support it are added, making the fuses below unseen.
At Mark III, it gains a proper cylindrical base, and the general color scheme is a blue-green one, as well as all seaweed being removed.
This is the only building that, apart from dealing damage normally, can also damage enemies when destroyed.
The explosion upon destruction is not subject to statue bonuses.
Apart from Hacked defenses, it's the only building that can damage another building.