You gain a +2 bonus to attack and damage rolls made with this whip, which appears to be made purely of sun-like radiance. You have resistance to radiant damage while this whip is on your person.

When you hit with an attack with this whip, the target takes an additional 1d10 radiant damage, or 2d10 if the target is a fiend or undead, and the target must make a Constitution saving throw (save DC 20) or be blinded until the start of your next turn.

Aura of the Sun. Shadows and darkness flee before the brilliant aura emitted by this whip. You can use a bonus action to cause the whip to stop emitting this aura, or to reactivate it. The aura extends 30 feet from you in all directions, but not through total cover. The aura is filled with bright light, which is sunlight, and it dispels magical darkness created by spells of 5th level or lower. A creature hostile to you or your companions that starts its turn in the aura or enters it for the first time on a turn takes 2d6 radiant damage.

Radiant Blade. You can use a bonus action to speak Blazeguard's command word and cause the radiant whip to shrink and partially solidify into a radiant mithral sword. In this form, it retains all of its features and traits, but functions as a longsword instead of a whip. You can use another bonus action to speak its command word and cause it to melt back into its whip form. If you are proficient with either longswords or whips, you are proficient with Blazeguard no matter its form.

Blazeguard has 12 charges, which can be used to fuel the features below. It regains 1d8 + 4 expended charges daily at dawn.

Retributive Flare. When a creature you can see within Blazeguard's Aura of the Sun hits one of your allies within the aura with an attack, you can use your reaction and spend 1 to 3 charges to deal 2d8 radiant damage to the attacker, plus 1d8 per charge spent beyond the first. A creature that takes this damage must also make a Constitution saving throw (save DC 20) or be blinded for 1 minute. A creature blinded in this way can repeat the save at the end of each of its turns, ending the effect on itself on a success.

Spells. While holding Blazeguard, you can expend some of its charges to cast one of the following spells from it: branding smite (2 charges), flame strike (5 charges), guardian of faith (4 charges), guiding bolt (one charge per spell level, up to 4th), and mass healing word (3 charges). You can also cast the sacred flame cantrip at will while holding this whip.
In addition, when you take the Attack action, you can forgo one of your attacks to cast a spell from the sword, expending charges as necessary. A spell you cast in this way must have a casting time of 1 action.

Proficiency with a Whip allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Damage: Radiant, Damage: Radiant, Resistance: Radiant, Blinded, Damage, Debuff, Utility, Combat, Finesse, Reach, Slow