Unlike the other two cards with this style of ability (Arcane Savant and Caller of the Untamed), if you have more than one Volatile Chimera in your deck, you need only reveal one of them because you can exile as many creature cards that aren't in your deck as you want, with a minimum of three. If you do reveal more than one Volatile Chimera before shuffling, you'll have to exile at least three creature cards for each of them.