“… because the “not entirely subtle” image of the hotel playground comes up as the top image in a google search for “not entirely subtle sandbox hint” …”

HA! This is hilarious! Spooky

Will publish the complete answer by tomorrow morning (my timezone);
Meanwhile, in a couple hours I will publish hint #3, which will remove all doubt about the answer, just so other people can choose to try their hand.

I believe Andrew got there with the full explanation first but I’ll go with;
Who will open your present, = I’ll go with present being a loose reference to prompt, and the fact sandbox will “open” with ./use
Make you play pleasant, = lets you test in isolation without affecting anything / anyone else.
Tidy your mess, = sbtool -o delete
Do the same for all else? = works equally well for all MySQL variants e.g. MariaDB, Percona Server

Okay, my initial shot was Query Optimizer but it’s a flawed answer which made me rethink.

I was also thinking that it could be the mysqld, it opens a connection (present == your presence on the server),
makes you play pleasant by parsing your query. If you’re not playing pleasant it will throw syntax errors.
Once parsed it passes your request to the query optimizer and it will ‘tidy your mess’ based on cost weight (explain extended::show warnings),
This is true of all connections.

But now I’ve seen the hints,
MySQL Sandbox – Will open your present or tar archive and bootstrap an instance,
Can effortlessly create environments for testing technologies such as M>S,MM and Circular replication (makes your play pleasant),
Master controls allows you to ‘tidy your mess’ when you’re finished, take down instances etc.
Does the same for all else…Percona Server, MariaDB, Oracle MySQL.

Maybe I’m bending this riddle into an answer.
Maybe there is no spoon.

😉