Crowns are secretly located game modifiers, found in hidden Crown Vaults. In order to access a Crown Vault you need to destroy a fully charged Proto Statue, this will spawn a portal to the Crown Vault. After touching the Crown Pedestal, you get to choose one Crown out of a set of six. You get a different set of Crowns before and after looping the game. You can also choose to not take a Crown at all. Crowns only last for your current run and disappear after restarting (which might be changed).
Currently, Crown effects do not stack. One Crown replaces the other, even if you take the same one twice. This goes for effects like more enemies spawning or pickups fading faster and being worth more.
Once you obtain a Crown, Cursed Weapon Chests will have a 1/7 chance to spawn in future levels of the current run. Having a Crown also causes I.D.P.D. to spawn right after you exit the Crown Vault and on 1-1 if you start with a Crown. A Proto Chest will spawn inside the Crown Vault if you already have a Crown when entering it.
Looping the game with a character that has a Crown will unlock it for that character and make it available right from the start. To unlock post-loop Crowns you have to loop twice, first to acquire a post-loop Crown and again to unlock it. All above rules apply if you start the game with a Crown selected.
Each time your character enters the Crown Vault you are presented with a set of six Crowns to choose from. If you started with a Crown, you will always have it as an additional option when choosing a Crown from the Vault.
There's a 66% chance that the Radiation Canister turns into a stationary Medkit at the beginning of a level, even if your character's health is full.
If you are below half HP the game still rolls a 50% chance to spawn the health chest, and if that doesn't work it rolls the 66% from the crown. This means that when below half HP the chance for a health chest to spawn becomes about 83.33% (1 - (1 - 1/2)(1 - 2/3)).
Crown of Guns
Disables ammo drops from enemies, (but not health drops).
Adds an 8% weapon drop chance to all enemies. Enemies that normally can't drop weapons will now have the added 8% chance.
As always, walking over weapons gives you an amount of ammo specific for that weapon that's equal to two Mini Ammo Chest pickups.
Heavy Heart further increases the enemy weapon drop chance by 210%. If an enemy had 2% chance to drop a weapon and Crown of Guns added 8%, then with Heavy Heart that becomes 10%+10*210%=31%.
Walking over weapons to get ammo and stationary Ammo Chests/Medkits are unaffected and give the same amount of ammo/health. However, using a portal to open stationary chests will give you mini pickups instead, which are affected by the Crown.