Sen Triplets

• WWizards of the Coast2020-08-07
  Official Ruling
  You can't activate abilities of cards in the target opponent's hand.
• WWizards of the Coast2020-08-07
  Official Ruling
  Abilities that create replacement effects, such as a permanent entering the battlefield tapped or with counters on it, are unaffected by Sen Triplets. Abilities that apply “as [this creature] enters the battlefield” are also replacement effects and are unaffected.
• WWizards of the Coast2020-08-07
  Official Ruling
  Activated abilities are written in the form “[Cost]: [Effect].” Some keyword abilities (such as cycling) are activated abilities and will have colons in their reminder texts.
• WWizards of the Coast2020-08-07
  Official Ruling
  Triggered abilities use the word “when,” “whenever,” or “at.” They're often written as “[Trigger condition], [effect].” Triggered abilities are unaffected by Sen Triplets.
• WWizards of the Coast2020-08-07
  Official Ruling
  Sen Triplets doesn't allow you to play more than one land during your turn or change when you may cast spells from the target opponent's hand.
• WWizards of the Coast2020-08-07
  Official Ruling
  The target opponent can't activate any abilities, including mana abilities.

Rulings via Scryfall