Idea I had a while ago, but didn't post.
Steam Vent: Active ability that creates a 1500 meter friendly cloud around the ship as it flies, but comes at a -70% thrust from all engines. Vision is obscured normally for both enemies and allies. Requires 3 seconds to form and to dissipate after activating.
The idea here is stealth, creating a cloud to hide in at either an ambush location or for attempting to survive after an ally falls. The obstruction of vision affects both the enemy and your own ship, requiring communication between captains in order to set up an effective ambush. This would encourage communication and strategy between allies, as well as creating a very interesting dynamic when attempting to escape. The extremely slow speed a ship would be forced to would cut it's maneuverability drastically, meaning that a ship could not simply vanish into the steam and race across the map.
Now, direct counter to it would be the flare gun, as it would completely eliminate the cloud and make the ambush a failure. That, and randomly shooting clouds, but primarily the flare gun.
For coding purposes, I figured you could have the cloud center on the hull repair point of the ship, as that would center it around a majority of ships as well as be somewhat lore-friendly (the main internal engine of the ship being dedicated to steam production, cutting power to engines).