While you could build a reasonable aggro or burn deck, people generally use it to try and make one-shot kills that take out the entire game at once
As the blue member of the cycle, it offers a free counterspell that delays creatures or planeswalkers without ever spending mana
If it is blocked, it deals this damage to the creature(s) that blocked it
These are from Promo Series A in Pokmon TCG Pocket
UnStable used watermarks as a new and improved version of that mechanic, neatly associating any diverse group of cards with minimal awkward templating or visual clutter
That means, instead of one more pack, you can guarantee a really great Stitch card, a card portfolio to match, and a bit of info on how to become a better player/collector