There are a few ways to influence casting cost, the cost-effective options are Thalia, Guardian of Thraben, Grand Arbiter Augustin IV, and Lodestone Golem
If you choose the second mode and the creature you don't control is not a legal target as Archdruid's Charm resolves, you'll still put a +1/+1 counter on your creature
Awaken the Maelstrom Baleful Mastery Black Widow, Agile Avenger Booby Trap Consecrated Sphinx Defacing Duskmage Faerie Mastermind Fate Unraveler Infernal Offering Kederekt Parasite Leela, Sevateem Warrior Malignant Growth Mathas, Fiend Seeker Mind's Eye Mind's Eye Nekusar, the Mindrazer Norn's Decree North Pole Research Base Notion Thief Ob Nixilis Reignited Ob Nixilis, the Hate-Twisted Orcish Bowmasters Pendant of Prosperity Razorkin Needlehead Red Death, Shipwrecker Saltwater Stalwart Sapphire Charm Sazacap's Brew Scrawling Crawler Sheoldred, the Apocalypse Smothering Tithe Tataru Taru The Unagi of Kyoshi Island Thief of Existence Trouble in Pairs Underworld Dreams Wedding Ring Xyris, the Writhing Storm Zurzoth, Chaos Rider
Still, they are pretty cool additions and add a lot more combo potential to the strategy
you can detached a Xyz material from this to negate the activation or destruction" If this card is detached from an Xyz monster to activate an effect: you can attach this card to an Xyz monster on your field as an Xyz material, or add this card to your hand during the End Phase
