Where as Unmask is a nice card, I prefer the 1 cost Thoughtsieze. Why? The exiling of the black card. Unless your starting hand has either 2 Animate Dead/Dance of the Dead/Necromancy (or a combination of the 3) there really is no room to be ditching the black cards of my build. Your black cards comprise: Your win-con, your mana accel (I use dark rits since I do not own any moxen) and an aide to your win-con (Buried alive, Entomb).

Sure, Thoughtsieze has a cost of 1 opposed to Unmask only costing the removal of a card. But, you can also make someone ditch a land, which can be crucial, especially against a control deck. Making someone toss a dual land can sometimes seriously throw off their mojo (Of course, this is all depending upon if your enemy has a hand of no moxen/lotus. But still, I think you can catch my drift.)

Another thing to keep in mind is card advantage. Tossing two cards to make someone toss one can be effective, if say you make them toss a win-con or a much needed accel card. However, with that, you are also bringing your total hand-size to 4-5, assuming you play it from your opening hand.

I'm by no means saying Unmask is a bad card. In fact, quite the opposite, especially in a control deck. As for Unmask in WGD (primarily the one that I run) I would caution against it, and keep the Thoughtseize in the SB.

Edit:
You said that Unmask is an outlet for the dragon. Did you mean, you can use the WGD to pay for the cost of Unmask? If so, you are wrong on two accounts.

1: Unmask reads (oracle):
You may exile a black card from your hand rather than pay Unmask's mana cost.
Target player reveals his or her hand. You choose a nonland card from it. That player discards that card.

WGD is a red card, meaning you cannot use it to pay for Unmask's cost.

2.: Even if you could pay for Unmask's cost with WGD, it would be exiled, not put in a graveyard. As Dance of the Dead, Animate Dead, and Necromancy can only target a creature in a graveyard, you cannot use the exiled WGD for the win.

If you meant something else entirely, then I apologize for misinterpreting your words.

I too am a WGD player. Ever since I first got my butt kicked by it on Magic Workstation, I immediately thought "Wow, I gotta make this deck!". 5 years later, it is -still- my most hatred deck, because of how quick it can work, and how effective it can protect itself.

Personally, I use Blue and Black WGD. Now, I have not been able to get any other power cards besides the Lotus, so this is by no means a "completed" deck. I have other things in life I must pay for, and now that I am married it is becoming even more difficult to buy power.

Anyway, here it is:

Creatures: 6

4x Worldgorger Dragon
1x Oona, Queen of the Fae
1x Ambassador Laquatus

Lands/Accel: 22

4x Underground Sea
4x Watery Grave
4x Verdant Catacomb
4x Forbidden Orchard
1x Black Lotus
1x Lotus Petal
4x Dark Ritual

Spells:

Black Spells: 14
1x Entomb
3x Buried Alive
1x Demonic Tutor
1x Vampiric Tutor
3x Dance of the Dead
3x Animate Dead
1x Necromancy
1x Demonic Consultation

Blue Spells: 18
x1 Ponder
x3 Standstill
x1 Brainstorm
x3 Daze
x4 Force of Will
x3 Careful Study
x3 Read the Runes

Sideboard: 15
x4 Deathmark
x4 Stifle
x1 Echoing Truth
x3 Thoughtsieze
x3 Cabal Therapy

This deck worked great in the meta I played in for years. I like the control aspect more. And when I say that, I mean the ability to control whether or not my opponent can disrupt my combo. FoW and Daze are amazing for this because they are free. The card advantage in this deck is astronomical. I know a lot of people have been ditching standstill, but I feel it is a very viable card in this version of the WGD. Since the object of the counters and disruption in this deck is to keep -your- stuff from being countered, it works very nicely. This deck is capable of turn 1, but you will more likely see wins on your turns 2-4, all depending.

There you have it. Some cards, like Entomb, I run 1 of becuase when i made the deck, they were restricted. Now, they are no longer, but as of right now I do not have the funding to drop $40-$50 on 2-3 more. But, if you are able to spend the dollars, I would recommend replacing the Careful Studies with Bazaar of Baghdad, and the Buried Alives with Entomb. Just a few suggestions.