Copycrook

Copycrook rulings:

2024-06-07: Except for the listed exception, Copycrook copies exactly what was printed on the original creature and nothing more (unless that creature is itself copying something or is a token; see below). It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or Auras attached to it, or any non-copy effects that have changed its power, toughness, types, color, and so on.

2024-06-07: If the chosen creature has  in its mana cost, X is 0.

2024-06-07: If the chosen creature is copying something else (for example, if the chosen creature is a Clone), then your Copycrook enters the battlefield as whatever the chosen creature copied, with the listed exception.

2024-06-07: If the chosen permanent is a token, Copycrook copies the original characteristics of that token as stated by the effect that put the token onto the battlefield, with the listed exception. Copycrook does not become a token.

2024-06-07: Any enters-the-battlefield abilities of the copied creature will trigger when Copycrook enters the battlefield. Any "as [this creature] enters the battlefield" or "[this creature] enters the battlefield with" abilities of the chosen permanent will also work.

2024-06-07: If Copycrook somehow enters the battlefield at the same time as another creature, Copycrook can't become a copy of that creature. You may choose only a creature that's already on the battlefield.

2024-06-07: You can choose not to copy anything. In that case, Copycrook simply enters the battlefield as a 0/0 creature and is probably put into your graveyard immediately, unless something else is increasing its toughness to keep it alive. It won't have "Whenever this creature attacks, it connives."

2024-06-07: Once an ability that causes a creature to connive begins to resolve, no player may take any other actions until it's done. Notably, opponents can't try to remove the conniving creature after you discard a nonland card but before it receives a counter.

2024-06-07: If no card is discarded, most likely because that player's hand is empty and an effect says they can't draw cards, the conniving creature does not receive a +1/+1 counter.

2024-06-07: If a resolving spell or ability instructs a specific creature to connive but that creature has left the battlefield, the creature still connives. If you discard a nonland card this way, you won't put a +1/+1 counter on anything. Abilities that trigger "when [that creature] connives" will trigger.