Ancient Viper

The Ancient Viper is a boss fought in the crypt, and one of the hardest in the game.

Frenzy
Goes into a Frenzy for about 15 seconds. During this, it will spin quickly to cut you off, closing any distance between it and the heroes, and use its frost/darkness bolts rapidly. This ability always ends with a Charge.

Darkness Bolt
Fires a bolt of darkness that predicts where the target is moving. If struck, the hero is Cursed.

Frost Bolt
Fires a bolt of frost that predicts where the target is moving. If struck, the hero is Slowed.

Darkness Explosion
Fires an extremely fast moving darkness bolt that strikes a larger area. Before using this, the Viper turns darker and takes a longer time to charge up the attack.

Frost Storm
Fires many frost bolts to cover a wide area.

Charge
The Viper charges at a hero after a short charge up. Deals damage to any hero caught in its path.

Strategy
To evade the Viper's regular attacks, you must dive (F + E) away from the bolt. This can be difficult because the Viper can spin around you and suddenly launch a bolt so you don't have much time to react and dive away. After Charging the Viper will be vulnerable for a few seconds as it is paused, so take that time to damage him as much as possible.

Charge is a very fast attack, and you may need to dive to get out of its path. Immediately after the Charge finishes, dive back in at the Viper, hit him once or twice, and then prepare to run because he's going to hit you with regular bolts now. If you get hit by a frost bolt, you will not be quick enough to get away and it will hit you over and over until it gets paused. If hit by a dark bolt, you will not immediately be able to heal from it.

Since avoiding each attack is so important, make sure you always have enough Stamina to dive away. The Viper's most dangerous attack is the Darkness Explosion, which travels extremely quickly. You can dodge this ability by either putting enough distance between yourself and it to begin with that the bolt reaches you with enough time to dive away, or diving twice in a row rapidly. Frost Storm can be treated like an ordinary bolt.

Rewards
You get a key to unlock the final lower crypt door, as well as a bounty scroll.