So. This happened.
Godly Flarion + Haste thingy. Now spams flarions at an insane speed, cannot actually stop it except by cancelling haste buff. Rather entertaining actually. Took out Duke Fishron and the Frost Moon bosses in a few seconds.
After more testing: Seems to be with any "punching" weapon (Flarion, Golem Fist, and KO Cannon). Also seem to be unable to use Magic Mirror with Haste Buff enabled.
MORE TESTING: All flails and punching weapons. And the Chain Knife.
Fishing Rods will throw out several hooks with no line, still retractable tho.
Able to throw out multiple Paladin's Hammers, they also have a much longer range than normal. Possessed Hatchet is fine though.
Drills will get stuck drilling. And float away from the player a bit. Normal picks are fine.
Bows and guns will fire multiple shots per click.
All Magic Weapons have their abilities enhanced to the point of ridiculousness. Example:
Yes, thats a stream of boulders. Also Magic and Ranged damage ISN'T halved... So...
Exceptions are the Crimson Rod and the Nimbus Rod, both of which summon several clouds but all but one and two (respectively) fade immediately. Also the magnet sphere, rainbow gun isn't buffed but there is a delay on its firing.
After more experimenting, Heat Ray and Golden shower are also unaffected, I think.
Summoning Weapons are unaffected.
Grenades are affected. Haven't tested bombs/dynamite since from grenade testing, it uses up about half a stack per click, and I'd rather not blow up my world.
Tested on new world. Both are affected.
North Pole seems to sometimes fire out
twoa lot of projectiles. Could be true for other projectile swords but its rather hard to tell, they go rather fast and unlike the NP they don't have snowflakes.
Terra Beam Projectiles seem to have decided that walls don't matter and often go through them.
Pirhana Gun... Well... Looks painful.
EDIT: Rod of Discord kills you upon use.
All this was done in Grovite Armor (Grealms) (+26% damage) with accessories and modifiers that bring it up 33% melee speed.
Okay thats about it, didn't go through every weapon but think thats most of them.