". . . you must open the gates of the Shredforge to all, but also . . ."

Persistent Petitioners

{1}, {T}: Target player mills a card. (They put the top card of their library into their graveyard.)
Tap four untapped Advisors you control: Target player mills twelve cards.
A deck can have any number of cards named Persistent Petitioners.

Ravnica Remastered

{1}, {T}: Target player mills a card.
Tap four untapped Advisors you control: Target player mills twelve cards.
A deck can have any number of cards named Persistent Petitioners.

". . . the communal bone garden is in dire need of new vertebrae, plus . . ."

Secret Lair Drop

". . . a decreased duration of synodic months would be most welcome. Also . . ."

Advisors that you haven't controlled continuously since your turn began may be tapped to pay for the second ability of Persistent Petitioners. This includes Persistent Petitioners itself on the turn it comes under your control.

It's not possible to tap one Persistent Petitioners to activate both its first and second ability, or to activate its second ability and that of another Persistent Petitioners. This means that if you tap four Persistent Petitioners, the target player mills the top twelve cards of their library, not the top forty-eight.

The last ability of Persistent Petitioners lets you ignore the "four-of" rule. It doesn't let you ignore format legality. For example, during a Ravnica Remastered Limited event, you can't add Persistent Petitioners from your personal collection, no matter how much they ask.