Quicksilver Elemental

• WWizards of the Coast2004-10-04
  Official Ruling
  If you make two copies of an ability that can be activated once a turn, you can activate each of them once a turn.
• WWizards of the Coast2004-10-04
  Official Ruling
  You can activate the ability more than once, collecting abilities from multiple creatures (or the same creature more than once).
• WWizards of the Coast2004-10-04
  Official Ruling
  If you use this card to gain Wall of Deceit's ability to turn itself face down, you will not be able to turn this card face up because it will not have the Morph ability.
• WWizards of the Coast2004-12-01
  Official Ruling
  Quicksilver Elemental can gain the activated abilities of any creature on the battlefield that you can target with its ability, even if you don't control that creature.
• WWizards of the Coast2004-12-01
  Official Ruling
  The granted abilities effectively use "this permanent," rather than "[that card's name]," so you treat the abilities as if they were printed on Quicksilver Elemental. For example, you treat an ability that says "Sacrifice a creature: Nantuko Husk gets +2/+2 until end of turn" as "Sacrifice a creature: Quicksilver Elemental gets +2/+2 until end of turn."
• WWizards of the Coast2004-12-01
  Official Ruling
  Quicksilver Elemental gains only activated abilities. It doesn't gain keyword abilities (unless those keyword abilities are activated), triggered abilities, or static abilities.
• WWizards of the Coast2004-12-01
  Official Ruling
  Quicksilver Elemental has a rather tricky interaction with Leonin Bola. You can actually unattach your opponent's Bola as part of the cost of activating the Elemental-copied ability.
• WWizards of the Coast2016-06-08
  Official Ruling
  Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keywords are activated abilities and will have colons in their reminder text.

Rulings via Scryfall