When using Slowking's "Opponent's Choice" Poke-POWER, do you have to show your opponent what the cards are since it says 'you may reveal the top 2 cards'?
Of course you have to show the opponent what the cards are. The "you may" refers to using the power, not to being able to use it without showing them the cards.
Source: Undaunted FAQ (2010-09-09), PUI Rules Team (2010-09-09)

Relevant cards

Note: All applicable cards may not be listed below.
HGSS3_85