Vipers are the snake-like, extremely dangerous enemies. This does not come from their offensive capabilities, but rather as a result of their two abilities, which they tend to use as often as possible. Those are:
- A tongue pull and binding attack. They can perform this attack from a long distance and it almost always ends as a success. The pulled soldier cannot move and will receive damage each round the binding effect lasts. You need to deal a few points of damage to the enemy to break the effect.
- Poison Spit. If the enemy is in range of at least two tightly grouped soldiers, or if all of your units are standing behind full cover, the Viper will use its spit attack. This has a chance of poisoning the target, dealing damage each round, which can be extremely dangerous, as the damage over time effects won't end on their own, they can only be cured with a Medikit. If you don't have enough Medikits, send the poisoned soldiers back to the base - the only exception to this rules is a situation in which you are certain that you can end the mission before the soldier dies.
You can use Flashbang Grenades while dealing with Vipers. Not only that they reduce the already moderate AIM of the enemy, they will also block all their abilities, turning them into almost harmless creatures. You should use soldiers with high AIM attribute when attacking Vipers, as their high DODGE allows them to receive only graze wounds, reducing the damage significantly.
If you cannot hit them with Flashbang Grenades, eliminating those enemies should be a top priority for your soldiers.