Hmm, for the Marines, disable their Personnel Cloaking.
For the Preds, have Hero Ghosts and Personnel Cloaking enabled, so they can cloak.
Hero Ghost = Predator with Spear Gun(requires Spears to shoot)
Dark Templar = Cloaked Predator using Wrist Spikes
Zealot = Predator using Wrist Spikes
Dark Archon = Maelstrom = Net Gun(they have no weapons out when using the Netgun)
Dragoon = Plasma Caster/Shoulder Cannon(Preds uncloak when using energy weapons)(requires energy to use)
You'd have to make a cloaking spell system... Because you can't ALWAYS be cloaked. You run out of energy.
Predator Items:
-Medi-Comp. They need energy to use this. Heals them 100%.
-Energy Sift. This recharges energy in full.
And when they use these Items, have them turn into a High Templar with no spells(for some amount of time)(aliens and marines get a minimap ping to your general location when you use these items - medi-comp makes you scream and Energy makes lound noise and bright lights)(*they can't run when using these items)
For the Alien players, have an observer that they can't move around following them. Why? Aliens can see cloaked predators because they "see" by pheremones.
FaceHugger = Egg(give like, 20 second hatch time, then they get a Chest Burster... not much else ya can do. The triggers would be too complex and no one would go near the damn Egg
Chest Burster = broodling. Have critters nearby(resawned when an egg is respawned) They need to kill something(as a chest burster) to upgrade into a different Alien. 3 critters = 3 different aliens. Read below.
Runner = hero zergling(super fast move/attack, less damage, less life)
Drone(what we see in the movies, mostly) = normal zergling(fast attack but no fast run, stronger attack)
Praetorian = normal Ultralisk(no speed boost, gets armor boost, even stronger attack)
Otional: Queen = Hero Ultra. MOST strongest). Become a Queen by killing the Queen as a Praetorian(comp will turn on you if you start attacking them) and become the Queen.
Have the Queen(comp) placed somewhere random(this is where Aliens will spawn) and the aliens must protect the Queen. She lays an Egg at set intervals. (if both aliens are dead, other aliens(comp) will help defend while you're waiting for rebirth) You have to wait for an egg to come back to life.
If you become a Queen, and you run from the nest to go kill stuff(im sure you will!) a computer controlled Egg appears. 20 seconds later, a chest burster. It kills the Critter that transforms it into a Praetorian, it waits for about a minute until it changes into a Queen, and the whole Egg/respawn cycle begins again.
Alien abilities:
-Headbite. Hmm, when a Marine/Predator dies, created a burrowed unit at the location, then they have to manual do the headbite(they have to do it quick before the body "disappears or becomes no good"). Heals them in full. Turn them into a Lurker Egg when feeding.
-Pounce(drone/runner/predalien only). Hmm, I have no good idea for this yet)
the only thing is you would have to make extended staircases for the Aliens because Queen and Praetorian... won't be able to get around much. To/From basement/upstairs.