On-screen use items

Make them unusable when there's no valid target on screen.

i.e. Jar of Souls shouldn't be usable when there aren't any mobs onscreen. Explorer's Key shouldn't be usable when there aren't any chests onscreen. Disposable Missile Launcher and Lost Doll could possibly be unusable when there aren't any mobs on the map.

Remind me if I forgot anything.

Edit: Pretty much any buffing item should be unusable if the teleporter's ready. Foreign Fruit should be unusable when at max HP.

 

I have to admit it is fun using the Missile Launcher when waiting for the cash to count down and seeing them as fireworks, but overall I think it would be a nice addition to save wasting the use

 

I believe that this would be a useful addition, as I cannot count how many times I've accidentally used explorers key.