The Ballista is one of the most useless units in the game. It's upgrades are very costly and it cannot fire at close range. This unit is reccomended for blowing away an unsuspecting group of waiting units, helping with razings, or if it is guarded by a few paladins.. Otherwise, its an easy target.
Don't underestimate the power of the Demolition Squad. Though essentially a suicide mission, a few of these guys in a transport unloaded on an island can take out a castle.
Though it has no armament, the Flying Machine can prove to be an effective weapon. It can get a good view of the map before Holy Visions or Eye Of Killrog, and it can also distract enemy fire and air attackers, as well as spot subs so your battleships can fire at them.
The Gryphon is a deadly addition to any force. Personally I keep a pen of them at my base and use them for defense only. I'll bring them out for my final blitzkreig assault or if i'm attacked by birds first. I have a tradition of not being a jerk by constantly air attacking. I don't like it, and I don't do it.
The mage is a somewhat weak unit. It's only redeeming quality is the effectiveness of the Blizzard. The other spells like Polymorph can be useful, but they take so much mana that they are slaughtered soon by vengeful friends of the sheep. These units are too costly and weak to be a major player.
As mentioned above, the mages aren't really a good idea unless you have tons of gold. Mages cost 1200 and blizzard 2000. After all this you could have gotten a few paladins and raided the base.
If you're on water, an excellent tagret would be the Oil Rig. It can't be repaired and its a sitting duck for subs. After it's destroyed, they come back to build another and you can sink that too.
The Paladin is a powerful ally. If you get enough Knights and upgrade to Paladin, this with armor and sword upgrades make them the ultimate attacking force. A group of 30 or so Level 7 paladins razing a base and healing each other at the same time will be almost unstoppable.
Peasants are a very versatile unit. Early on you should crank out a ton of these guys to get an early supply of gold and lumber. They are also good, in large numbers, for dispatching an invading Footman or two.
If you want an early way to shut someone down, use this method. First of all, you need to know where they are right away. If you do, then build a barracks first then a farm. After that build up a bunch of footmen and destroy the other guy's base before he even has soldiers built.
Once fully upgraded, the Battleship can be a very powerful land and sea unit. It's perfect for flattening seaside guard towers and units with one or two shots. Used together with Flying Machines or Gryphons, they can sink a sub in one shot.
The Archer, once upgraded to Ranger, is the perfect way to destroy a large Gryphon-ed enemy. Just send over 20 or 30 of these guys to do the work. If you succeded, the archers can also destroy the town.
The Submarine may not be the strongest sea unit, but with it's subversiveness it can be very useful in stopping the enemies sea force all together in one attack. If you keep them planted off the coastline, they can never start again!
Transports are great in one-on-one multi-player. Grab these fast and put one peasant on unsettled islands. Soon you will have a giant war machine capable of anything. Transports are also perfect for loading with Paladins and creaming these tiny, unprotected little gold factories, however.
If you follow my advice, you'll be destroying the enemy in no time.
