Does Yordle Explorer trigger to draw a card when you play Switcheroo from Hidden (which has a printed power cost of 2 but costs 0 when played from Hidden)?

Ruling: Yes, Yordle Explorer will trigger and draw a card when you play Switcheroo from Hidden.

Nuances:

• Cards that check costs look at the printed value on the card, not the actual amount paid to play it
• You don't have to pay the full cost for the trigger condition to be met
• This works the same way as Lux triggering on discounted spells