Psychic Venom

A blue damage source built entirely around the opponent's agency, which is itself a strange thing for blue to be. The Aura sits on a land and waits, turning the enchanted player's own mana usage into a slow bleed: every tap is two damage, and that player is usually the one choosing when to take it. The mechanic is a punisher in the strict sense, collecting whenever the enchanted land taps and idle until it does. That framing has aged poorly as a tempo proposition (two mana to maybe deal two a turn is a rate the game outgrew within a few years), but the design itself is the interesting artifact: direct damage built around restraint, printed in a color that would soon retreat from burn almost entirely. The closest spiritual relatives are the lands-that-hurt-you effects (Manabarbs, Zo-Zu the Punisher, Ankh of Mishra), but those tax every land in play; this one taxes a single land, repeatedly, and only when used. It is the smallest, most surgical version of the punisher idea, and one of the few times blue was allowed to wear that hat at all.