The Executioner was a massive, amorphous mutation created from the mass of HO213 and serves as the first boss of Extermination. Encountered by Dennis beyond the drawbridge, it consists of a rather formless main body that covers the wall and a large tentacle with three segments.
Its main attacks are crushing Dennis with its body. In the first attack, the tentacle will rise high an twirl its head, then slam down above Dennis three times. It moves slower then Dennis so a timed dodge each time before it strikes will leave him unscathed. Its second attack is more deceptive, swerving its head to the side as if its going to sweep Dennis, but this is only a fake-out for the actual move. Once it sweeps its head the first time, immediately run to the opposite side of the arena, and out of the second swing's reach. If it swings its head once and you are still beneath it the head will slam down. If you get too close to its core (which is positioned at the base of the tentacle and exposes itself only a few seconds at a time) it will release infectious gas.