The Undead Warrior Ghost almost is a new monster, being that it skips the green axes entirely. Especially when mobbed together, their axes pass through their comrades and make for quite a volley.
Golem ghosts are nigh pointless when placed in high-visibility areas. Typically they end up just being more annoying to kill, since the Crossbow's small arrows are going right through them and diminishing the already slim chance of one-shotting.
It's not until they're paired with Undead Warriors that they really start getting interesting. When your Golems are frontlining, you can't have them shielding you from flying axes. Strategy!
They're also suitable when placed in dim areas textured in a similar color. The camouflage effect makes it all the more necessary to use your ears.
Going back to Starscream's suggestion, I think it's been well-established how happy we are about modifying the existing monsters too much.
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