Marked For Death
From Worms Knowledge Base
A worm that is marked for death will receive double damage one time, meaning the effect is removed after the damage has been done. Being marked does not remove other status effects, so the worm flicker between different colors to show the multiple status effects one has. This effect will make the worm appear purple, with a skull above its name tag, while having the name tag flash purple. Being marked stacks with the fury effect, so the worm will suffer even more damage if it has both of these status effects - bringing damage to be +80% of the original damage amount. Being marked while a worm is zombified will have the damage alterations cancel each other out, bringing the damage to be only +10% of its original damage.
There is nothing that can remove being marked for death before taking damage - not even collecting health crates.