Mirror monster cards can be found in Play Boosters and Collector Boosters
They help keep cards safe from dust scratches and daily wear
In those days, Mana Drain wasnt strictly better than Counterspell, thanks to mana burn, and it really did come up sometimes
Just look at this How does one evaluate a card like this in a draft where you can also open Sol Ring, Swords to Plowshares, Flash, Ancestral Recall, The One Ring, Ragawan, Force of Will, Lightning Bolt and all the other very, very powerful cards that are in the Vintage Cube
1 Dreamstone Hedron
This is all neatly tied together with Fallaji Archaeologist and Thundertrap Trainer , who help you find the missing pieces and act as sacrifice fodder for Flare of Denial