Ascension Key

In order to access The Ancient Tower from the overworld, one must present an ascension key to unlock the tower’s main door. The keys were handed down to the demons of Asmodeus, in order to leave them the option to communicate to those in Aetheris, and therefore by extension the gods themselves. The keys are shaped like two-headed spears, making them also effective as a weapon. Each of the 26 cities in Asmodeus has been granted at least one set of keys. By tradition, one demon would be selected in every city to be the key bearer. These key-bearers would wield the key into battle and be the ones to ascent to Aetheris in case the need arrived. Most of the cities would safeguard their additional key or keys in a secure place. In the case of Mausolea, The Locked Altar was chosen as the keeping place of their extra key.
To make use of an ascension key in combat, its wielder must be attuned to it. This, however, can only be done using a rare kind of crystal, called Voidprism which grows along the edges of Asmodeus where the abyss meets the demonic land. An ascension key acts as a bident that can be used as a spellcasting focus, it's damage acting as magical damage for the sake of immunities and resistances. Additionally, the key possesses two features that can be activated at will: Shifting Magic, and Enhance Armorment.
Shifting Magic: When casting a spell using the key, the wielder may choose to change the nature of the spell. An ascension key can change the damage type of a spell to one of 4: fire, necrotic, psychic, or force. Whichever typing the spell takes depends on the key's wielder, as the nature of the spell changes to whichever type the caster is most attuned with. This will be the type of which they know or have used the most spells. If multiple types are about as representative of the caster's magic as each other, then the typing of the spell is determined randomly between them each time a spell is cast using this feature.
Enhance Armorment: Once per long rest, a creature wielding an ascension key is able to enhance any one weapon, including itself. Weapon attacks made with the enhanced armament deal extra damage equal to the proficiency bonus of the key's wielder. Alternatively, the key's magical power can be enhanced. Magical attacks with the weapon or spell cast through this weapon will deal an additional d4 of damage per level of the spell slot used. The type of this damage is the same type as determined in the shifting magic feature. The enhancements last for 24 hours, or until the key's wielder takes a long rest.
Using an ascension key in battle without being attuned to it will make the edge appear dull, allowing it to hit for only 1d4/1d6 piercing damage, which is not counted as magical damage. Additionally, the key cannot be used as a spellcasting focus without attunement.

Ascension Key
Type	Weapon, melee
Rarity	Very rare
Requires attunement	Yes
Damage	1d8/1d10 piercing
Properties	Thrown (20/60), Versatile, Finesse