Three "Ancient Leaf" can trigger "Spell Absorption" while also making use of the added life points for more draw power, three "Goblin Thief" are a dream card to use with "Fire Princess" due to supporting both the burn strategy via healing as well as inflicting damage on its own, three "Ledger of Legerdemain" can fetch more of the necessary cards via draw and the deck is able to stall enough to make that work, three "Swords of Revealing Light" are further stall options and also give a "Spell Absorption" trigger, two "Child's Play" help protecting "Fire Princess" while providing more healing for the "Cure Burn" strategy, three "Cauldron of the Old Man" provide constant healing/burning, three copies of "Dark Sanctuary" provide further protection while also inflicting damage, one "Terraforming" serves as a fourth draw for "Dark Sanctuary", one "Poison of the Old Man" serves as more healing/burning, one "Mystical Space Typhoon" against pesky backrow and one copy of "Magical Mallet" to shuffle unnecessary cards away while also providing another "Spell Absorption" tick

The effect is worth it at the beginning of most games
For just 2 mana at instant speed, it makes all your permanents hexproof and indestructible until end of turn
Mega Gengar EX is currently one of the top chase cards in Pokemon TCG Pocket that you can pull from the Mega Shine Expansion
Attacking is possible when your opponent's memory is at 1 or more