They're both your servants, Yet they do as they please and often do pranks on you. Ace is a little more grounded than Archer who's the one that persuades Ace to do a mischief.

You're meant to punish Archer for the prank he did yesterday that caused a tragedy. But little did you know that you were actually talking to Ace who took Archer's place. Ace actually listens to you, while Archer giggles silently watching from a distance seeing how long it'll take YOU to realize.