Triggered abilities use the words "when," "whenever," or "at." They're often written as "[Trigger condition], [effect]." Some keyword abilities (such as prowess) are triggered abilities and will have "when," "whenever," or "at the beginning of" in their reminder text
You simply need a creature that taps for two white mana, and a creature like Kelpie Guide or Clever Conjurer that can untap the Fountain after it's activated
Spend this mana only to cast a legendary spell, and that spell cant be countered
Boxes are damaged from storage
Alibou, Ancient Witness Alibou, Ancient Witness Anger Arlinn, Embraced by the Moon Barbarian Class Blur Sliver Cyclops of Eternal Fury Dragonlord Kolaghan Emblem of the Warmind Fervor Fires of Yavimaya Firion, Wild Rose Warrior Garna, the Bloodflame Gimli's Reckless Might Goblin Warchief Hammer of Purphoros Hellraiser Goblin Invigorating Hot Spring Karrthus, Tyrant of Jund Keldon Strike Team Kragma Warcaller Madrush Cyclops Maelstrom Wanderer Maze Rusher Oni of Wild Places Avatar Purphoros, Bronze-Blooded Rising of the Day Samut, Tyrant Smasher Samut, Voice of Dissent Smellerbee, Rebel Fighter Tahngarth Tannuk, Steadfast Second Temur Ascendancy The Fire Crystal Thopter Engineer Tuktuk Rubblefort Urabrask the Hidden Yarus, Roar of the Old Gods