For 4GG, you reveal the top seven cards of your library and look for any one of twelve relevant keywords (haste being the one Kathril doesnt mention), putting a creature with one of those keywords onto the battlefield and the rest into the graveyard
If the target creature's power is still less than the power of the creature with mentor, put a +1/+1 counter on the target creature
They also work nicely with Coastal Piracy effects and anything else that rewards you for hitting your opponents
Every box guarantees 1 Trainer SR, 3 Art Rares, and 4-5 Double Rares
However, Wizards of the Coast have stated that not only can this card only be found in Collector Booster packs, but also that it only appears in less than 1% of Collector Boosters overall
This allows the attack " Prismatic Blade " to be used out of nowhere