play merry havoc with

child's play

Something particularly easy or simple.

go on one's merry way

To depart.

go play in the traffic

To go elsewhere and feel free to engage in risky behavior; to get lost.

grandstand play

A successful play or other manoeuvre during a sporting competition in which one or more players shows off unnecessarily in order to entertain or impress the spectators.

hold-up play

A play where an attacker retains possession of the ball, while the teammates can move up the field.

Merry Andrew

A person who clowns publicly; a buffoon; an entertainer's assistant.

merry dance

A useless waste of time resulting from a deception.

merry men

A group of assistants, subordinates, or lackeys