This level is filled with a dreadful silence...
Just like a "khe khe" level, only instead of barrels are Cysts.
Cyst = dark red barrel. Upon damaging it explodes like a fuel barrel. Releasing a random level-appropriate enemy, or a group of weaker ones.
To add to the horror feeling, each cyst has also % (10%?) chance to trigger when player moves/acts just next to it.
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Upon leaving the stairs, you trip on some kind of a wire. Alarms sound in the distance.
All enemies on the level get "tagged" by a player, just like if he'd damage them. Efficiently making everyong hunt the player.
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The space around you seems to be strangely warped.
Level boundaries (outtermost walls) act as "wrappers". Possibly might have a "shimmering" property, changing colors. If you try to enter such tile, it translocates you to the opposite side of the level. Cannot be generated on cave levels.
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You see a red-headed demon fiddle with some machinery. Sunddenly an alarm sound echoes through corridors...
A nuke is set on the level, just like in Ao Red Alert - basicly AoRA mode for 1 level.
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Walls on this level are made of cardboard...
All walls, except the outter boundaries of the level, got 1 point of structure strength - you can destroy them even with a basic pistol, or by walking up against them if you're in a running mode.
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Walls on this level are made entirely of glass sheets...
Translucent walls. Easily destroyed by enemies trying to shoot through or break through (moving towards wall tile has chance to destroy it).
When wall is destroyed, it causes slight damage to all surrounding tiles (yes, can cause chain-destruction of walls this way).
For all practical reasons, this is like an "empty" level regarding visibility, with some additional tactical options.
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Edit: combined several posts into a single one, as per request of thelaptop.