Is there a list of variables that you can change to modify gameplay?
Ones I know of are:
g_gravity
g_speed
g_humanstage
g_alienstage
g_humanstage2threshold
g_alienstage2threshold
g_humanstage3threshold
g_alienstage3threshold
g_humanbuildpoints
g_alienbuildpoints
g_suddendeathtime
g_suddenDeathTime
timelimit
What more do you know of?