Sac outlets and Illusionist's Bracers are this girl's best friend
You still cast the cards as face-down 2/2 creatures for 3 mana, and you can turn them face-up for their megamorph costs as a special action
At a glance, the card doesn't seem that powerful, countering a one-mana spell for one blue mana or, thanks to its Phyrexian mana cost, two life
Pulling this specific Charizard runs far longer, since each set has several SIRs and you are hunting one of them, which pushes the realistic odds for this exact card into the hundreds of packs
Any card abilities which happen when a player pays a cost to use them (activated abilities) or automatically when specific conditions are met (triggered abilities) must also pass through the stack and can be responded to the same way (though you would need a card that says target ability to interact with one)
This is a good example of how slabs can hide whats wrong with a card