Brave-Kin Duo can target your Emberheart Challenger without actually expending additional cards
One standout so far is Betor, Kin to All (2WBG), a powerhouse that triggers different effects at the end of your turn based on the total toughness of creatures you control
Ian Malcolm, ChaoticianIan Malcolm, Chaotician tips his toe into the chaos pool, giving everyone access to every one else's cards one at a time, and only if someone draws more than one card per turn, though if you stuff your Ian Malcolm deck with cards like Dictate of KruphixDictate of Kruphix, Howling MineHowling Mine, and Temple BellTemple Bell, you can reliably grow the pile of extra spells you can cast
Added are effects that buff your entire team including Heraldic Banner and Goblin Surprise, allowing you to dish enormous damage and attack for victory
Then, later, in 601.2f, you check what its cost is
If your squad creature is countered then it never hits the battlefield, and the triggered ability never happens