I'm going to go over all of what has currently been revealed in how they work, both mechanically and Ruling-wise
Detailed pages, types, stats and your favourite Pokmon - on the app
With seven cards in the SIR line, TCGPlayer states that there is a one in 32 chance of finding one of these cards, although that number jumps to one in 225 if searching for a specific one, such as this Giovanni's Charisma card number 204/165

Ruler of the Skies Museum 1 The first Ruler of the Skies Museum Secret Mission involves collecting all of the Full Art One Gold Star for this booster pack: Wurmple #156 (Full Art/One Gold Star) Lileep #157 (Full Art/One Gold Star) Kricketune #158 (Full Art/One Gold Star) Accelgor #159 (Full Art/One Gold Star) Ponyta #160 (Full Art/One Gold Star) Quilava #161 (Full Art/One Gold Star) Kyogre #162 (Full Art/One Gold Star) Samurott #163 (Full Art/One Gold Star) Raichu #164 (Full Art/One Gold Star) Wattrel #165 (Full Art/One Gold Star) Clefairy #166 (Full Art/One Gold Star) Ralts #167 (Full Art/One Gold Star) Wynaut #168 (Full Art/One Gold Star) Oricorio #169 (Full Art/One Gold Star) Anorith #170 (Full Art/One Gold Star) Poochyena #171 (Full Art/One Gold Star) Gulpin #172 (Full Art/One Gold Star) Vullaby #173 (Full Art/One Gold Star) Genesect #174 (Full Art/One Gold Star) Dragonair #175 (Full Art/One Gold Star) Noivern #176 (Full Art/One Gold Star) Cyclizar #177 (Full Art/One Gold Star) Raticate #178 (Full Art/One Gold Star) Aipom #179 (Full Art/One Gold Star) Rewards: 36 Wonder Hourglasses, 12 Pack Hourglasses and 10 Shop Tickets

Once per turn, during the End Phase, if both players control the same number of monsters: Destroy this card
X from Majestic Dawn.