These are temporary modifications that last for a single level. They can affect many different items e.g. reduced player speed, increased visibility, more aggressive enemies.
You will initially start the game with 5 of these unlocked:
A new one will be unlocked at level completion for every 500 enemies that are killed. You do not need to collect skulls for this to happen, the act of killing the enemies is enough – however, if you rewind time, any kills during that period will also be undone!
The player must kill a certain number of enemies in a set time to be aware of a transient glitch – this counter will reduce over time so it’s beneficial to play fast and aggressively to be aware of these.
The gauge will no longer deplete once the target number of kills is reached or all enemies on the level are killed – it will turn white to indicate you’ve reached the target amount.
You can then choose an item at random from the ones you have unlocked after the shop phase has completed.