Five mana is a little steep for aggro decks, but clearing a blocker and making an opponent lose life is kind of like giving Dalek Drone haste
Having a second enchant creature on the list is clearly a sign that these decks played things pretty safe as far as two-player games of Magic go, but Grim Reapers Sprint incentivizes you to cast it at a point in the turn where you would expect your opponent to have already fired off their removal spells
If you are a fan of the Dressrosa arc, then youll want to pick up this Kyros while it is cheap
Cards that just hard counter a spell that targets the creature, like Kira, Great Glass-Spinner, definitely exist but theyre much less common
Second, unlike Panharmonicon, which really needs to be built around, since Naban, Dean of Iteration is already an on-curve creature, we can get away with playing fewer enters-the-battlefield creatures while still making Naban, Dean of Iteration powerful