Dyskairos

Dyskairos is an FPS with simple retro-styled visuals inspired by roguelikes and metroidvanias. Ascend a mysterious Tower, while battling its current and former inhabitants, discovering an arsenal of weapons and abilities, and uncovering the source of the force holding you prisoner. All the while, the clock is ticking and the Cycle will continue...
An Unfortunate Expedition
You suddenly find yourself stuck in the vicinity of a structure known only as the Tower. The Crystal that powers your travel suddenly breaks and you become stuck. Fortunately, somewhere within the Tower is a replacement.
The Tower won't make it easy for you, however. It will oppose you at every opportunity. You are not the first traveler to get stuck here... and you probably won't be the last.
The Cycle Will Continue
Once you trespass inside, the Tower begins its Cleansing Cycle. You'll only have minutes until it climaxes. Once it does, the contents of the tower will change: enemies will resurrect, items will shift around, passages may become blocked, and keys to progression may appear in different locations.
For a Traveler such as yourself, adaption is the name of the game; as the Tower's Cycles continue you will have to extract what you can, and abandon what you can't.
Fortunate Allies
A group of people equally as mysterious as the Tower - known only as "Townsfolk" - live on the Tower's outskirts. Also affected by the Tower's Cycles, they share part of your goal. They will provide you with shelter from the Cycle and may even dare to rescue you, should you fail to escape in time.
Experienced in dealing with stranded Travelers, they have all the amenities you require for success. Collect scrap material and bargain for upgrades, store weapons and upgrades for future use, or pass the time with quaint dialogue. What the Townsfolk lack in initiative, they make up for in stoicism.