Descend is a new rules term that refers to times that a permanent card is put into your graveyard from anywhere
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
Legendary Creature - Wizard Efreet Doubler (CTRL to add secondary) Dungeon Ellywick Tumblestrum +1: Venture into the dungeon
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
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