It does come with a cost, since you will also do 200 damage to your Roaring Moon, leaving it with max 30HP
Anafenza, the Foremost Archive Haunt Bloodchief Ascension Catlike Curiosity Centaur Vinecrasher Compost Countryside Crusher Dennick, Pious Apparition Dimir Strandcatcher Disa the Restless Duskmantle Guildmage Dutiful Knowledge Seeker Forbidden Crypt Lazav, Dimir Mastermind Lorcan, Warlock Collector Nihilith Planar Void Profane Memento Quest for Ancient Secrets Robot Domination Sand Scout Sefris of the Hidden Ways Skola Grovedancer Slogurk, the Overslime Soulcipher Board Syr Konrad, the Grim Tamiyo, the Moon Sage The Dark Barony The Gitrog Monster The Haunt of Hightower Turntimber Sower Ultron the Annihilator Ultron's Auxiliary Voracious Brood Vulturous Zombie Yuma, Proud Protector
Instead of just dropping one and hoping it survives, support cards help protect them, make their abilities stronger, or speed up how quickly they gain loyalty
With these two card types being very important for setups, Arven makes it easier to access them as soon as you can start playing Supporters
Pokemon Mega Greninja ex Premium Collection