The Swarm

A_FREAKING_DUCK

This idea is based on a huge swarm of a few dozen of a new type of creature, all about the size of a crash. They are parasites that aren't just found in a certain place, but after a long time playing, they all come swimming at high speeds to your base (or cyclops, or whatever is man-made of yours). They're main purpose is to give a reason to add defense to your base, as they stick onto the walls and deal quick damage, causing many floods. In order to defend from these creatures, your going to want a new perimeter defense system added to your base. This can do 2 things, one similar to the seamoth, zapping everything attached to the base(designed almost solely for the swarm, but can get rid of floaters if they happened to attach on) and knocking it off, possibly killing it, and it has a cool-down of 15 seconds. The other is a turret that fires a bolt which damages enemies within the bases vicinity, but fires slowly and requires ammo. Keep in mind it can be destroyed, but repaired with a welder. You can also fend these creatures off using normal means of harming enemies, but they do attack you if you get close. They can also infiltrate the base, crawling around on the inside destroying lockers and such, and those that made their way inside are not effected by the defense systems and must be dealt with yourself. This would give a reason for security cameras as well. Because flooding would be common during these rare attacks, it would give a reason for hatches in ladder passages as well, acting similar to bulkheads, except to keep the flood from flowing upward through ladderways. If you were too new to the game to not be prepared or were simply not ready, and these creatures are destroying your base completely, they will eventually leave after a few in-game days(as they are meant to be dealt with by hand, not by waiting, of course). This is all for this idea currently, I will add more if anything comes to mind!