Red
Let's start off with Red. I like to call Red "Creature offense." What this means is that it focuses on the creatures: dealing damage to your enemy's creatures and buffing your own creatures to overwhelm their defense and strike at their life points. As such, Red is effective against breaking through defensive decks. However, it is vulnerable to debuffs that affect life or power, because Red uses a good amount of power to work and because it has few Instants that actually heal yourself or directly hurt your opponent.
Recommended against: Blue, Purple
Not Recommended against: White, Black
Creatures:
Red is heavily creature based, so it has a good supply of 3-strength hard hitters. Buff these guys up to do a ton of damage.
Scythian Footsoldier: 1R cost, 1 strength. Your basic soldier/cannon fodder. The main perk about these guys is that you can buff them for more damage, and you can use them to activate Scythian Elite or Commander J'Ardan's special power, which I will go over later. Still, buffs are better spent on other stronger units, so use these guys as disposable shields in the early game so that you can summon your more powerful troops.
Veteran Mercenary: 2R cost, 2 strength. Another basic unit. Just like the Footsoldier, but stronger and better.
Recon Drone: 2R cost, 1 strength, unblockable. Recon Drones are pretty useful in that they are unblockable. As such, buff these guys and use them to assault your opponent's lifepoints. Shielding with them would be a waste; use only as a last-ditch resort.
Scythian Disruptor: 2R+1 cost, 1 strength. I don't really like these guys, because they're quite weak and their special ability really isn't that useful. You can sacrifice them to destroy a modifier. Your opponents usually don't use modifiers, or use them in very silly ways, but still, it can help you remove your opponent's offensive or defensive edge, should you really need it.
Scythian Blade: 3R cost, 3 strength. These guys have a pretty poor special ability. If you're going to sacrifice them, you might as well use them to attack whatever you want dead with three damage instead of two. Blades, however, make great shields, because of their high strength; you can actually keep them alive to fight for you.
Scythian Elite: 2R cost, 2 strength. Scythian Elite are pretty good. They gain 1 strength if you have three or more soldiers, and it can really give you that offensive edge you need to survive.
Commander J'Ardan: 3R cost, 1 strength. J'Ardan is the best Red creature. He gains 1 strength for every soldier you have in play, so if you fill up your side with soldiers, you get 1+5 (6) strength. He has a deck limit of 2 because of his sheer awesomeness.
Scythian Artillery: 4R+1 cost, 5 strength, penetration. Artillery is the powerhouse of the Red side. Combined with Hypermobility, it will annihilate your opponent. It has penetration, which deals excess damage after blocking onto your oppenent's life points, so it is also effective against defensive units like the Myrkin Bureaucrat or the Solarian Fortress with Rally.
Instants, Modifiers, and Auras:
Hypermobility: 3R, modifier. It makes a unit unblockable. Use on hard hitters like Artillery, Commander J'Ardan, or Scythian Blade.
Targeted Shot: 3R, instant. An indispensable card for breaking through defensive lines. It does three damage to a target, perfect against Bureaucrats, Fortresses, and Shield Walls.
Battle Cry: 3R, aura. It gives all your units +2 strength during your turn. Perfect for that final push to destroy your enemy, or for holding the line.
Medic: 2R, instant. It heals 2 life. What can I say? Anything that heals your life with only a power cost is good.
Rally: 2R, modifier. It increases one of your unit's strength by 2. You can use on practically any unit, but I recommend using this on your unblockable Recon Drone, or to combine this with Hypermobility to really pack a punch on your enemy's life.
Armageddon: 4R, instant. You unlock this after beating the Scorched Earth challenge. It kills all creatures in play, even your own. As a result, use this as a last resort if you're really getting your ass kicked. I don't include this in my deck, since I made it before I beat this campaign; you can live without it anyway.
Firestorm: 4R, instant. It deals one damage to all your enemy's creatures. Perfect for softening them up, or for eroding your enemy's defense. It is particularly effective on Purple, because they have a large number of 1 strength units that can be speedily eliminated with Firestorm.
Heavy Weapons deck
I call my Red deck "Heavy Weapons," because that's basically what it is: Blast away your enemy's defenses and assault their life points. You can also call it Blitzkrieg or Steamroller. Here it is:
5x Scythian Footsoldier
5x Veteran Mercenary
2x Commander J'Ardan
5x Medic
3x Scythian Elite
5x Targeted Shot
4x Hypermobility
3x Battle Cry
4x Rally
4x Firestorm
4x Scythian Artillery
4x Recon Drone
4x Scythian Blade
4x Scythian Disruptor
4x Memory Serpent
Your first point of action is to build up your forces. Keep building up power, summon your first troops, but don't attack. You need to preserve your life points so that you don't get knocked out before you get a chance to get the big guns out. Once you've reached 5 power, you can start drawing cards. Unleash your Elite and Commanders to power them up. By this point, your opponent probably has a defensive line. Use Targeted Shot to weaken the high power defend-only creatures, then finish them off. Use Memory Serpent, Rally, and Battle Cry as needed to make mincemeat of creatures and life points alike. With any luck, you should be able to overwhelm the enemy before they get a chance to hit your life points.