Possible Quest Puzzle Mechanic

I just had an idea for a puzzle mechanic.
While they don't usually accept quests, they're probably always looking for mechanics/ideas right?
Ehe. Anyways.
Starting off I'm going to just throw some probably trash lore behind this so it makes a little more sense.
You need a thing.
Thing is in a box.
Box belongs to NPC.

[1/6] NPC: Oh you need my thing?
[1/6] NPC: It's in the lockbox over there.
[3/6 NPC: The combination is... is....
[4/6] NPC: Well darn I just can't seem to remember. Maybe I wrote it down?
[NPC looks around]
[5/6] NPC: I'll keep searching, while I'm at it you can play with the fish. They're Fish Names.
[6/6] NPC: Unlike the Blue Tang, they have a great attention span, and memory! They'll copy most patterns they see!

You'll go over to the fishtank and right click the NPC, opening a chest GUI that has water and a bunch of fish.
The fish will spell out the number pattern of the combination.
There are other possible uses, this was just an example.

 

That would require plugin changes, which is not likely to happen for something this small.