Agatha of the Vile Cauldron
Legendary Creature — Human Warlock
Activated abilities of creatures you control cost 
less to activate, where X is Agatha's power. This effect can't reduce the mana in that cost to less than one mana.
: Other creatures you control get +1/+1 and gain trample and haste until end of turn.
Jason A. Engle
Wilds of Eldraine Promos (PWOE)
• #199pRulings
Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities are activated abilities and will have colons in their reminder text. Triggered abilities (starting with "when," "whenever," or "at") are unaffected by the cost reduction ability of Agatha of the Vile Cauldron.
(wotc • 2023-09-01)
Agatha of the Vile Cauldron's first ability affects only abilities of creatures you control on the battlefield. The costs of activated abilities of creature cards that work in other zones (such as cycling) won't be reduced.
(wotc • 2023-09-01)
Rulings
Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities are activated abilities and will have colons in their reminder text. Triggered abilities (starting with "when," "whenever," or "at") are unaffected by the cost reduction ability of Agatha of the Vile Cauldron.
(wotc • 2023-09-01)
Agatha of the Vile Cauldron's first ability affects only abilities of creatures you control on the battlefield. The costs of activated abilities of creature cards that work in other zones (such as cycling) won't be reduced.
(wotc • 2023-09-01)