Aliens
Bring several drones along with any hunting parties. You can use them
to drop hive nodes as you move along, enabling you to regenerate any
units that become wounded by enemy resistance. Moreover, hive nodes
see just like other aliens, enabling you to track any enemies that
cross your prior path. Finally, if you upgrade your drones, their
cystic acid spittle ensures that any hosts you subdue will produce
offspring of stronger stock than normal.
Cheat menu
To unlock Cheat Mode, pause the game and press R, R, L, R, L, L, R, L, R, R, L, R, L, L, R, L. Now, a number of Cheats will be available from the Options menu:

Cheat Win
Clear Fog of War
Enable All Levels
Gimme $10,000
Player Invulnerable
Show LZs
Toggle Unit Spying
Defense Mode
when ur being the marines and there in defense mode there health will grow little by little and there attack will be stronger.
Predators
Try sneaking up on and attacking a lone enemy with a cloaked Spear Master and see what happens