Wyvern/1.03

Wyvern are advanced fliers. Wyverns are rarely seen, with only High Elves, Dark Dwarves and Plague Lords having access to them, but that probably is a good thing. Not only do Wyverns have good stats across the board, but they can inflict fear, too. All this, plus the capability to attack all targets, makes this flier a real monster! Although, the piercing typed attack does leave something to be desired when it comes to attacking buildings.

Dark Dwarves
Wyverns are great units and arguable the best advanced flier in the game. (Pterodactyls have better stats but can't inflict fear and can't attack ground targets - probably why they went extinct.) Dark Dwarves were truly gifted when they were given Wyverns as their advanced flier as these great creatures can help them out with what Dark Dwarves really need - speed. A 15 speed stat is pretty good as it is, but that can be upgraded with the Golden Wyvern skill, pushing it to 18! With such speed and infantry killing power, Wyverns can quickly cut ahead of the enemy and act as a painful deter between them and your vulnerable siege weapons. The added trait of causing fear can worsen the enemy's luck, dropping their attack power and making your units seem that much more durable.

Unfortunately even Wyverns have their downside. Firstly, their attack type leaves them unable to break buildings, although this isn't much of a problem for Dark Dwarves as pretty much everything else in their arsenal, including their basic flier, can demolish buildings with ease. But it does mean that they can't simply be let loose on the enemy base and rain terror. Secondly, one of their two resource costs is shared with a siege weapon. The cost of producing Wyverns along side the top-end siege weapons can be quite demanding, although it doesn't clash in any way with the two common Golems - Stone and Iron. So, really, even their weaknesses aren't all that bad.

The Golden Wyvern research is specifically for the Wyvern and it also benefits from Armorer and Mithril researches.

High Elves
The High Elves got greedy in WBC3 and snagged themselves a second advanced flier, and one which doesn't even get banned when the No-Fliers rule is implemented.

The Wyvern is a powerful unit and one of the best fliers in the game, but its piercing damage type offers nothing new to the High Elves. This alone gives it large competition with the Pegasus, who usually comes out on top in regards to choice. If the crushing damage that the Pegasus brings to the table isn't in much need, but still in need of a strong flying unit, then the High Elves can choose to produce Wyverns over Pegasi for the raw power that they hold, even though it might be advisable to train a small flock of Pegasus to get the chance to stun an enemy Titan or tough Hero. Otherwise, producing them together is a little redundant, as the excess resources could be saved for an actual Dragon.

Plaguelords
Wyverns are actually pretty good. But unfortunately for the Plaguelords, they cost gold and crystal, and a lot of it. It's that one and only reason why Plaguelords rarely use them, otherwise they would be a great addition to the Plaguelord ranks - offering a piercing attack to help keep Orcs at bay and using their speed to hit priority targets fast and relocate their position at a moments notice, greatly helping overcome the Plaguelords natural lack of speed. Before producing some, you really have to consider how much it will harm your economy to do so, and decide what is truly needed at that time.