Which weapons can't have legendary modifiers?

Solution 1:

The following melee weapons cannot have any of the "Melee" attributes (Legendary etc). Boomerangs, Flails, Spears, Chainsaws or Drills (including the Hamdrax). They can only have attributes from the "Universal group, which every single weapon can have (the highest universal modifier is Godly).

This means that tools, so long as you swing them like a sword, can have Legendary status.

The only two weapons that can never have modifiers are the Light Disc and the Bananarang, most likely due to their stacking ability.

The Star Cannon and Clockwork Assault Rifle can have the regular "Ranged" modifiers except for any that include + or - knockback, as they inherently have 0 knockback. This means that they can't have Unreal etc. The Magical Harp works the same way, meaning that it can never be Mythical.

This page has all the info on reforging and the modifiers that come with it that you will ever need.