You can roll this die to regain a certain amount of hit points based on what you roll plus your level (I was going to do times half your level but i'm not sure about it yet). If the hit points you gain exceed your hit point maximum, the remaining points can be turned into temporary hit points (to a maximum of 15 points) that last until your next long rest. Each number rolsed increases the amount of d4s you roll for health (1 to 4 like potions of healing). The die can be used four times before it becomes inert for 7 days.

Die of Hardening (D6)

You can roll this die to gain a bonus to your armor class based on what you roll for 1 hour. Your skin also changes appearance depending on what you roll. Only one bonus can be applied to each creature and cannot be stacked until the current bonus dissipates. Every two numbers from 1 to 6 is a different bonus (+2, +3, +4). Same again with 7 days but used three times.

You can roll this die to gain resistance to a certain type of damage for 1 hour.

1. Piercing

2. Slashing

3. Bludgeoning

4. Fire

5. Cold

6. Lightning

7. Poison

8. Acid

Same usage and days as above

You can roll this die to gain a spirit companion that can aid you on your journey for 8 hours. I used humanoids and beasts of CR 1 to 3.

 

All of the spirit companions share these traits: they share your initiative in combat, they obey only your commands, all of their attacks are magical, and they have resistance to non-magical damage. Same days but two uses.

You can roll this die to gain the ability to cast a spell. The result also shows how many times you can cast that spell (three, two, or one time based on what leveled spell it is). The spell stays with you until your next long rest or when you cast all its uses. The spells are cast at their base level. You use your highest mental ability score for casting the spell. Same days and uses as above.

You roll this die for a wondrous effect to happen, such things like gaining darkvision for 5 hours, or turning into a dragon for 1 hour. If you roll a 15 or higher, there is a 15% chance that the die becomes inert for 1 year. Same days but it's one use.