Alright, everyone, including @phoenix. Here’s the Project 154 saga. (Created by Diseased Productions.)
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it starts with the game’s protagonist, Gamma-Class Bio-Weapon Project #154, in a containment cell with a doctor. He kills the doctor and shoots out the ventilation shaft above the room. After fighting his way through numerous guards throught the building, especially in a large elevator, he makes it to the exit where Poseidon is guarding. After defeating him, Project 154 breaks free. Later, he learns of Zeus and Hades pursuing him with the intent to kill him. He then makes it to a small rooftop exit, where a dead Poseidon-like entity lays in a puddle of blood. The entity jumps him, and a “To be Continued” is then displayed across the screen.

The identity of the entity on the roof is never explained, but it can be assumed that this was Zeus before his design was finalized. (All of this literally copied and pasted from https://thing-thing.fandom.com/wiki/Thing-Thing_(game).)
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This is ONLY part 1 of the Project 154 saga.
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Part 2 is coming soon. These games are from the 2000’s. From 2005 to 2008. (Thing-Thing Arena games are from 2006 to 2013. Disappointing ending.) You guys think so too?