The Mirror comes down in the mid-game and ramps up fast, often drawing your four or five cards a turn by the end of the game, and rarely running you more than 3-4 mana to get in play
The only problem with it is that because you're capped at one damage per draw, you're quite likely to deck yourself before you kill everyone at the table (in a four player Commander game, that is.) You're not locked in however
Also, you can use the cards in your hand to link, which raises the DP, allowing even small Digimon to battle and activate various effects
Because they are promotional and limited, their value may increase over time with proper care
And disbalance occurs when it's used with cards to fill discard piles
Leaf Storm doesnt do much better with four whole Energies to deal 60 and heal your Grass-type Pokemon on the bench a little