During either player's turn, when your opponent activates a card or effect that targets this face-down monster: You can change this card to face-up Defense Position
The ideal reactive board is actually Formula Synchron into a Black Rose Dragon, or Trishula, Dragon of the Ice Barrier to summon it on the opponent's turn
your opponent takes no battle damage this turn, also you Special Summon 1 "Raidraptor" Xyz Monster from your Extra Deck in Defense Position, but its effects are negated, also return it to the Extra Deck during the End Phase
Rivaz of the Claw is, however, a Rakdos leaning Dragons-matter creature
Therefore, the card is only really played in Hammer these days , in which its used as a toolbox for various equipments like Colossus Hammer, Kaldra Compleat, Shadowspear and others
Chimchar [Reverse Holo] #31 (Pokemon Twilight Masquerade | Pokemon Cards) prices are based on the historic sales