A burglary took place at the headquarters of Les Pyjamasques: the moon crystal has disappeared. While Les Pyjamasques kept framing Sorceline for seizing it, it was Roméo who did it, so he can increase its powers.
The following characters appeared in the episode "Romeo's Crystal Clear Plan":
You should not just accuse someone for what they didn't do.
When Romeo inserted the moon crystal into his machines, they only made good things happen:
Shoot a purple rocketing fire.
Grow sweet smelling flowers.
Make stuffed toys and sweets appear.
When Romeo inserted the moon crystal into Robot, he gains new powers but also turns his back on Romeo, before Luna Girl pulled the moon crystal out of him.
Though Romeo was the culprit, Luna, despite not having a plan, decides to repetitively trap the PJ Masks once she gets her Moon Crystal back as the PJs fight both her and Romeo over said crystal. Therefore, just because the PJs let Luna know about the crystal does not mean she briefly helped them before trapping them.
Even PJ Robot didn't know about the culprit until he presumably saw Romeo show up in front of the PJs and Luna through the PJ Picture Player.
When the moon crystal was inserted into PJ Robot, it made clones of him.
Luna Girl’s Luna Wand makes its fourth appearance.