Kadena's Silencer
Creature — Snake Wizard
When this creature is turned face up, counter all abilities your opponents control.
Megamorph (You may cast this card face down as a 2/2 creature for 
. Turn it face up any time for its megamorph cost and put a +1/+1 counter on it.)
Torstein Nordstrand
Commander 2019 (C19)
• #8Rulings
Triggered abilities use the word "when," "whenever," or "at." They're often written as "[Trigger condition], [effect]." Some keyword abilities (such as madness's ability to cast the exiled card) are triggered abilities and will have "when," "whenever," or "at" in their reminder text.
(wotc • 2019-08-23)
Kadena's Silencer counters only activated and triggered abilities already on the stack. It doesn't prevent abilities from being activated or from triggering later in the turn, and it has no effect on static abilities.
(wotc • 2019-08-23)
Activated abilities are written in the form "[Cost]: [Effect]." Some keyword abilities (such as equip) are activated abilities and will have colons in their reminder texts. Notably, turning a creature face up is not an activated ability.
(wotc • 2019-08-23)
If you counter a delayed triggered ability that triggered at the beginning of the "next" occurrence of a specified step or phase, that ability won't trigger again the following time that phase or step occurs.
(wotc • 2019-08-23)
Abilities that create replacement effects, such as a permanent entering the battlefield tapped or with counters on it, can't be countered. Abilities that apply "as [this creature] enters the battlefield" are also replacement effects and can't be countered.
(wotc • 2019-08-23)
Kadena's Silencer can't counter an activated or triggered mana ability. An activated mana ability is one that could add mana as it resolves, doesn't have a target, and isn't a loyalty ability. A triggered mana ability is one that could add mana as it resolves and triggers on an activated mana ability.
(wotc • 2019-08-23)
Rulings
Triggered abilities use the word "when," "whenever," or "at." They're often written as "[Trigger condition], [effect]." Some keyword abilities (such as madness's ability to cast the exiled card) are triggered abilities and will have "when," "whenever," or "at" in their reminder text.
(wotc • 2019-08-23)
Kadena's Silencer counters only activated and triggered abilities already on the stack. It doesn't prevent abilities from being activated or from triggering later in the turn, and it has no effect on static abilities.
(wotc • 2019-08-23)
Activated abilities are written in the form "[Cost]: [Effect]." Some keyword abilities (such as equip) are activated abilities and will have colons in their reminder texts. Notably, turning a creature face up is not an activated ability.
(wotc • 2019-08-23)
If you counter a delayed triggered ability that triggered at the beginning of the "next" occurrence of a specified step or phase, that ability won't trigger again the following time that phase or step occurs.
(wotc • 2019-08-23)
Abilities that create replacement effects, such as a permanent entering the battlefield tapped or with counters on it, can't be countered. Abilities that apply "as [this creature] enters the battlefield" are also replacement effects and can't be countered.
(wotc • 2019-08-23)
Kadena's Silencer can't counter an activated or triggered mana ability. An activated mana ability is one that could add mana as it resolves, doesn't have a target, and isn't a loyalty ability. A triggered mana ability is one that could add mana as it resolves and triggers on an activated mana ability.
(wotc • 2019-08-23)