Please note: all credit goes to Kermit The Frog!
This guide will show you how to kill red death at 30 minutes.
Guide to Kill Red Death
Step 1: Defeating Moongolow and Obtaining the Yellow Sign
First you need to unlock Moongolow, this is done by getting to 25 minutes and defeating the boss that spawns on any 4 stages.
Next you need to go to Moongolow and get to 14 minutes as a non-secret character and a special boss will spawn.
You need to defeat this special boss, after the boss is defeated you will get teleported to a stage called “Holy Forbidden” where you need to progress to the end without dying and pickup the drop in the beam of items at the end past the wall of the regular map.
Step 2: Killing Red Death
Once you have unlocked the Yellow Sign you are ready to head into a stage to kill Red Death.
I recommend using Inlaid Library as it is the easiest stage in Vampire Survivors.
Once you spawn in you should notice additional floor pickups on the sides of the map, you need to prioritize getting to these or else you cannot kill red death.
Once you get the items in your inventory you need to max them out and make sure you take and max out laurel and clock lancet once they are maxed pick up chests to evolve them into crimson shroud and infinite corridor.
I recommend using a strong beefy character for this so you have a higher chance of success, move clockwise around red death when you get there so that the clock lancet freeze beams emitted by infinite corridor are consistently freezing death in place.
Once you have defeated red death you will have unlocked the “Mask Of The Red Death” character.
Note: empty tome is good for this because it speeds up the freeze beams, and every time you beat red death you get 5 free golden eggs.