Scientists Aang's Journey Absorb Vis Ainok Guide Analyze the Pollen Ancient Excavation Archaeomancer's Map Ash Barrens Assassin's Trophy Atalan Jackal Attune with Aether Avengers Disassembled Bant Panorama Battle Plan Beamsaw Prospector Beanstalk Giant Beneath the Sands Bioengineered Future Biomechan Engineer Biotech Specialist Bitterthorn, Nissa's Animus Borderland Explorer Borderland Ranger Borough Backup Boseiju Reaches Skyward Boseiju, Who Endures Bountiful Landscape Braidwood Sextant Brave the Wilds Brokers Hideout Bushwhack Cabaretti Courtyard Campus Guide Canoptek Wraith Caravan Vigil Case of the Shattered Pact Centaur Rootcaster Changeling Wayfinder Civic Wayfinder Cleansing Wildfire Colossal Collision Coming Attraction Compass Gnome Contaminated Landscape Cycle of Renewal Dance of the Tumbleweeds Dauntless Scrapbot Dawntreader Elk Deathsprout Deceptive Landscape Deep Reconnaissance Demolition Field Dig Up Diligent Farmhand Dire-Strain Rampage Dismissive Denial District Guide Divert Disaster Double Play Dreamscape Artist Druid of the Emerald Grove Dune Mover Earthbender Ascension Ecologist's Terrarium Edge Rover Edge of Autumn Elanor Gardner Elfhame Sanctuary Embermouth Sentinel Embodiment of Spring Emergency Eject

For most players, that is a feature, not a bug
Mechanically, they could move counters between other creatures that represent their parasitic larvae, and perhaps have healing or protective effects on the "host" creature - unless the host is black-aligned
The 'cards in hand' thing is the lamest text I can find on a Magic card
Unlike Adventures, however, you dont get the best of both worlds since the card is shuffled away after playing
Collectors Boosters are available to pre-order in boxes of 12 packs for $429.99 from Amazon and Best Buy