The Hell Is This

Wield the loose piece of floor as a weapon, with the key in your off-hand.

There's no need for any "off-hand" mechanic. You can just put the key in your inventory and use it whenever necessary.
Wielding the piece of the floor as a weapon, on the other hand (heh, hand), might actually be a good idea.

You obtain the ENIGMATIC KEY.
You equip the LOOSE FLOOR TILE.

Take the key from between your legs and... Stab the door? Was there even a keyhole?.... Stab the door anyways.

You guess you might as well see if you can do something about that locked door with this key. You turn around-



But there's only silence.



This is becoming less okay by the minute.

Take the E from between your legs and turn it into an F

This isn't the time for stupid jokes, you're seriously creeped out here!