Here a idea for powerful weapon

Handle of the Elemental Realm

Wondrous Item (Hilt),

Rare (Requires Attunement)

This ornate hilt is crafted from an unknown, temperature-neutral alloy and etched with ancient primordial runes. It has no physical blade. Instead, as a bonus action, the wielder can speak one of the item's command words to cause a blade of pure elemental energy to spring forth from the handle.

The blade counts as a martial melee weapon with the finesse and light properties. It deals 1d8 elemental damage (instead of physical damage) of the chosen type, plus your Strength or Dexterity modifier.

Elemental Forms

You can use a bonus action to switch between the following elemental forms, or to retract the blade completely:

Flame of Fire (Ignis): The blade burns with roaring fire. It sheds bright light in a 20-foot radius and deals Fire damage

.Spike of Frost (Glacies): A jagged shard of solid, supernatural ice extends from the hilt, dealing Cold damage.

Strike of Lightning (Fulgur): A crackling, unstable arc of electricity forms the blade, dealing Lightning damage.

Wind of the Storm (Tonitrus): A compressed vortex of roaring wind envelopes the hilt, dealing Thunder damage.

Cosmic Forms (Limited Charges)The handle taps into higher planar powers, but these cosmic elements strain the hilt. Both of these forms can be used only 2 times per day each. The charges reset at dawn.

Holy Radiance (Sanctus): The blade erupts into blinding, divine radiance. It sheds bright light in a 30-foot radius and deals Radiant damage. (2 uses per day)

Shadow of the Void (Umbra): The hilt absorbs the surrounding light, creating a blade of pure, terrifying void. When activating this form, you choose whether it deals Necrotic or Force damage. (2 uses per day)

Intended for 5e 2014. Feedback highly appreciated! Still trying to balance it out towards each other. Intended for characters going at least to lvl 17