Druids of the Claw are mixed units. In Bear Form they are an advanced melee unit such as an Abomination, Knight or Tauren. In Night Elf Form they are a spell caster such as a Priest, Sorceress, or Shaman. Druids of the Claw are initially in Night Elf Form. You must research Druid of the Claw Master Training to turn into Bear Form. Druids of the Claw are very useful additions to your army in both forms. In Bear Form they can be up front tanking as a melee unit while Druids of the Claw in Night Elf Form take up the rear casting Rejuvenation and Roar.

After you have upgraded to Tree of Ages build an Ancient of Lore which you can use for Dryads and Druids of the Claw. Build one Druid of the Claw and send him to your army and use Roar. Roar gives a 25% bonus to damage to all of the units in the area with only one cast. You may have to pack units tightly into a small area to have Roar cover them all since it has a small area of effect when cast.

If you plan to build a lot of Druids of the Claw it can be very difficult to transition to them. It's far more challenging to upgrade to Bears than Knights, Tauren, or Abominations. One possible option is to just create a Hero and use it to harass the enemy early on while you upgrade straight up to Bears. To do this build a Huntress Hall and no Ancient of War and then lay down two Ancients of Lore once you reach Tree of Ages. Then continue to upgrade to Tree of Eternity and research Adept and Mastery upgrades. This can work if you can confuse and harass the enemy until you get upgraded while keeping them away from your town. Another option is to make a bunch of Archers without upgrades and use them until you can convert to Bears. Another option is to play normally but go get an expansion pretty early. Build lots of Moon Wells and two Ancients of Lore and two Hunter's Halls to research both upgrades at once.

It's very important to prevent Druids of the Claw from dying using Rejuvenation. It's very expensive and time consuming to replace lost Druids of the Claw. The best way to do this is using subgroups. Watch the portraits of the Bears while having the Rejuvenation icon active. Select Rejuvenation and click on the portrait of the damaged Bear to heal him. You can also use the "Alt" key to watch for low hit point bars.

Some players like building a lot of Druids of the Claw but leave them in Night Elf Form. While they don't do as much damage as they would do in Bear form they can cast Rejuvenation on themselves and Roar. Usually when focusing on Druids of the Claw it's best to mix them up having most in Bear Form and some in Druid Form to cast Rejuvenation and Roar on the Bears. Research Mark of the Claw so that you can use Roar while in Bear Form.

Druids of the Claw cannot attack air units so be aware of this weakness. Druids of the Claw and Archers with range upgrades are a good combination.

Use Moon Wells to build up the Druid of the Claw's mana so he can cast his most powerful spells right away. Then send him off into battle.

Vs. Spell Breakers
Use Roar to waste mana so that the Spell Breakers cannot use their Feedback against you. While it may seem against your best interest to use Roar because of the Spell Steal, in reality it will work in your favor if you keep spamming it.

a) you will run the Spell Breakers out of mana
b) you will have more units Roared than the enemy, since it is an AOE buff, and Spell Steal is single target
c) less mana on your bears = less feedback damage