There is a PCQ next saturday and there is something I want to have perfectly clear:

My opponent has the iniciative and passes me the priority.

At this point, I want to play two effects. Can I play both effects before giving back priority, or must I pass priority after the first (and then play the second one when my opponent passes)?

Thanks in advance.

It depends a bit on what the two effects are. If you're talking about something like Nasty Surprise and Overload, you have to let NS resolve, since Overload's targetting requirement makes it so the character must be pumped before you can play it. In a case where the two cards are not dependant upon each other, such as playing Tech Upgrade and Signal Flare to get your hands on Mr. Fantastic (5) and a Fantasticar, it's perfectly fine to chain both effects before passing priority.

If you've got a specific example that still eludes you, I'll be glad to help with it.

Thank you a lot. I was under the delusion the non-active player had to pass priority after playing an effect. I wonder where did I get that idea from.

So, you never give back priority until you are done playing effects, no matter who the active player is. That's a good thing to remember!

You may have been thinking about when effects resolve. After an effect resolves, regardless of who generated it, the primary player will get priority.

So, using Canamrock's example, if the opponent plays Mystical Paralysis on your character and passes, you can play Tech Upgrade and Signal Flare without giving up priority. However, when you pass and your opponent passes back, the Signal Flare will resolve. Your opponent (being the primary player) now has priority to add an effect to the chain before you can, even though it was your effect that just resolved.