Arcane Box of Spellloading

"Hey, I know how much you hate using your spell slots for....uh.....not......fireball......but I think I've found a solution! Just store your spell in this box for later! Just uhh.....make sure to write down what spell you put in."    -Phanphelver, disgruntled elven artificer.

The Spell box is a small, obsidian black cube the size of a Rubix cube, with golden crossing livery.

Any spell caster can expend a spell lot of appropriate level to store a spell inside the cube. Only one spell can be stored at a time in the box. When the box is opened (see opening the box below) the box immediately casts whatever spell is stored inside on the closest creature (almost always whoever opens it) regardless of what kind of spell it is. The box uses its own spell save DC (DC=15) and spell attack bonus (+5). The box can hold concentration on spells for either 5 turns (based on whoever opened the box) or whenever the spell is supposed to end (whichever option is shorter). 

OPENING THE BOX: Upon discovering the box, players make two skill checks: The first skill check is a DC 17 arcana check to determine what the box does and what spell is currently loaded inside (see recommendations below). The spell identify immediately bypasses this check. The second check is a DC 13 investigation check to attempt to solve (and open) the box. Rolling a natural 20 on the previous arcana check or using the identify spell bypasses the need for the second role. 

OPENING THE BOX (continued): Players who succeeded both checks can choose whether if they want to activate the spell loaded in the box. Failing the arcana check but succeeding the investigation check causes the player to open the box unknowingly and causes whatever spell is loaded in the box to activate and casts it on the nearest creature. Failing the investigation check but succeeding the arcana check results in nothing, but the player who rolled the investigation check can attempt it again after a short rest. 

AFTER OPENING THE BOX: Once the box has been opened, anyone who has previously succeeded on an investigation check for the box can open the box without issue. Opening the box and triggering the spell takes a bonus action during combat, but an action to load a spell back into it. 

RECOMMENDATIONS: The DM gets to choose what spell is loaded in the box upon discovery from any class spell list and up to any level of spell. If you want to be funny, choose something like banishment, grease, darkness, thunderwave, hold person, etc. 

And if you hate your players, put a 9th level disintegrate spell into the box.