Fireboy and Watergirl

Fireboy and Watergirl is one of the most beloved browser-based co-op puzzle games ever made. Originally created by Oslo Albet and Jan Villanueva, the game features two characters — Fireboy (who can walk through fire but is destroyed by water) and Watergirl (who can cross water but is hurt by fire) — who must work together to solve environmental puzzles. Set across multiple elemental temples including the Forest Temple, Ice Temple, and Crystal Temple, each stage presents unique challenges involving switches, doors, moving platforms, and color-coded elemental hazards. While designed for two players sharing a keyboard, it can also be played solo by controlling both characters alternately. The game's clever design perfectly balances cooperation and individual skill, making it an enduring favorite for friends and siblings.