This idea will probably be too hard to add in due to the number of things that'll need to be changed and/or added but damn it I want to play a smaller version of Sid Meier's Alpha Centauri! Also keep in mind that times and distances are chosen at random for use as examples and should be disregarded post haste.
Polyp*: One of your colonists discovers a strange red polyp growing near the colony. It appears to use grow on and breakdown rocks for nutrients and may be able to damage our walls. (Once the events starts a single tile somewhere near the edge of the map gets turned into Polyp. The Polyp expands one tile in every direction every 1-2 days. Things like walls, tables, chairs etc etc that are next to a Polyp tile are dealt a small amount of damage over time but will prevent Polyp from spreading onto that tile. Polyp can be cleared by a colonist with the growing skill or a flame weapon.)
Spawn Thrower: If a Polyp tile is left alone for a set period of time (a few days, maybe 5?) it may transform into a Spawn Thrower (provided no other Spawn Thrower is within a set distance away). After being left along for a period of time, the Spawn Thrower will then launch a Spawn pod thingy (highly technical name, natch) in a random direction and up to a certain distance away. On landing the Spawn pod will transform every tile within 3 tiles of the landing site into polyp.
*or Xeno Fungus, depends on what'll get you sued I guess.
Polyp*: One of your colonists discovers a strange red polyp growing near the colony. It appears to use grow on and breakdown rocks for nutrients and may be able to damage our walls. (Once the events starts a single tile somewhere near the edge of the map gets turned into Polyp. The Polyp expands one tile in every direction every 1-2 days. Things like walls, tables, chairs etc etc that are next to a Polyp tile are dealt a small amount of damage over time but will prevent Polyp from spreading onto that tile. Polyp can be cleared by a colonist with the growing skill or a flame weapon.)
Spawn Thrower: If a Polyp tile is left alone for a set period of time (a few days, maybe 5?) it may transform into a Spawn Thrower (provided no other Spawn Thrower is within a set distance away). After being left along for a period of time, the Spawn Thrower will then launch a Spawn pod thingy (highly technical name, natch) in a random direction and up to a certain distance away. On landing the Spawn pod will transform every tile within 3 tiles of the landing site into polyp.
*or Xeno Fungus, depends on what'll get you sued I guess.