We can all agree that Terraria is a fun game, but it's not perfect. One aspect that frustrates me is the plethora of weapons at your disposal, but the inability to use all of them effectively. Wouldn't it be great if you could simply tap a button and instantly cast a Magnetic Sphere without having to switch out your current weapon? How about using Golden Shower to debuff the enemy quickly? Or maybe tossing a grenade? Or using a magic mirror to escape and deadly situation?
Sure, you can always have these items on your hotbar to use, but more often than not, it proves a time waster as items won't switch out unless the animation is complete. Using the mouse wheel also proves problematic at times. I rarely use my Magnetic Sphere anymore for this reason.
The answer is to simply have a set of 5 (or more) customisable hotkeys that you can use for one-time casts that maximises your combat effectiveness while making it more interesting, and makes your life easier. Each hotkey would have the same cooldown as the items (their firing speed) but would cast quickly, albeit not simultaneously if you pressed all of them at once.