Midround Antag Event: Martian Invasion.

[Glamurio]

Martians are dying out, doesn't really make sense lorewise for a small force (That lost already) to take on NT regularly?

Depends on the way you view it. "Regularly" implies there's a continuity between shifts, which isn't really that guaranteed considering it's been the same year for many years. If anything, this "martian invasion" event could be a last ditch effort of the remaining forces to attack. Not to mention, new lore about cloning technology improvements (perhaps with outside assistance) could be introduced that could explain the sudden influx of martians.