Monsoon

The damage line reads as symmetrical: at every end step it taps each player's untapped Islands and bills that player for the count, controller included. The parity is a fiction of wording. A Gruul deck running few or no Islands pays nothing while leaning the full weight onto a blue opponent, and the tap clause is where the cruelty lives. Tapping a blue player's Islands at the end of their turn strips their ability to hold up mana across other players' turns: no counterspell backup, no instant-speed answer, no held trick while they sit tapped out. Those Islands untap on their own turn, so this is not a tax on casting; it is a leash on reactive play, with a recurring burn bill stapled on top. That double penalty (tempo theft plus damage scaling to the manabase) marks the card as land-hate from a design philosophy since abandoned, back when blue could be punished for the simple act of running blue. Its ceiling and floor are both dictated by the opponent's land choices: a devastating clock against a heavy-Island deck, a dead enchantment doing nothing for its four mana against a board with no Islands at all. Total blowout or total blank, an all-or-nothing axis that later design deliberately engineered away from, replacing blunt color hosers with effects that cost the controller something too.