Curiosity

The original "draw on hit" enchantment, and the template that every card-advantage aura since has been measured against. The design idea is a single conditional that pays you for connecting: stick this on something hard to block (an evasive flier, a creature with menace, anything the opponent cannot profitably trade with) and combat damage stops being a clock and starts being a draw engine. The trigger fires per instance of damage, not per turn, which is the detail that turns it from a midrange value play into a combo enabler: any creature that deals damage to an opponent twice, or pings repeatedly, repeats the draw, and players have spent years pairing it with effects that grant unlimited attacks or repeated direct damage to bury an opponent in cards. What balances that rate is the card's fragility. It lives on the creature, so any removal spell two-for-ones you, and a chump block on the wrong turn leaves it doing nothing. Wizards has revisited the exact text more than once: Snake Umbra and Keen Sense ported it into other colors, with Snake Umbra stapling on totem armor, and Tandem Lookout reprinted the effect on a creature with soulbond. None of those changed the core proposition Curiosity established, which is that one blue mana can convert evasion into a hand refill for as long as the creature survives.