Hulking Metamorph

• WWizards of the Coast2022-10-14
  Official Ruling
  Any enters-the-battlefield abilities of the copied permanent will trigger when Hulking Metamorph enters the battlefield. Any "as [this] enters the battlefield" or "[this] enters the battlefield with" abilities of the chosen permanent will also work.
• WWizards of the Coast2022-10-14
  Official Ruling
  Casting a prototyped spell isn't the same as casting it for an alternative cost, and an alternative cost may be applied to a spell cast this way. For example, if an effect allows you to cast an artifact card without paying its mana cost, you could either cast Blitz Automaton normally, or as a prototyped spell.
• WWizards of the Coast2022-10-14
  Official Ruling
  The prototype ability functions in any zone that the spell could be cast from. For example, if an effect allows you to cast artifact spells from your graveyard, you could cast a prototyped Blitz Automaton from your graveyard.
• WWizards of the Coast2022-10-14
  Official Ruling
  If the chosen permanent is a token, Hulking Metamorph copies the original characteristics of that token as stated by the effect that put the token onto the battlefield, with the listed exceptions. Hulking Metamorph does not become a token.
• WWizards of the Coast2022-10-14
  Official Ruling
  When cast as a prototyped spell, that spell has the mana cost, power, and toughness characteristics shown in its colored, secondary text box rather than the normal values of those characteristics. Its color and mana value are determined by that mana cost. The permanent that spell becomes as it resolves has the same characteristics. If the spell leaves the stack in any other way, or the permanent it becomes leaves the battlefield, it immediately resumes using its normal characteristics.
• WWizards of the Coast2022-10-14
  Official Ruling
  If an effect copies a prototyped spell, that copy (as well as the token it becomes on the battlefield) will have the same characteristics as the prototyped spell. Similarly, if an effect creates a token that's a copy of a prototyped permanent or causes another permanent to become a copy of it, the copy would have the same characteristics as the prototyped permanent.
• WWizards of the Coast2022-10-14
  Official Ruling
  Regardless of how it was cast, a prototype card always has the same name, abilities, types, and so on. Only the mana cost, mana value, color, power, and toughness change depending on whether the card was cast as a prototyped spell.
• WWizards of the Coast2022-10-14
  Official Ruling
  When casting a prototyped spell, use only its prototype characteristics to determine whether it's legal to cast it. For example, if Blitz Automaton is exiled with the last ability of Chandra, Dressed to Kill, you would be able to cast it for (because it's a red spell), even though you wouldn't be able to cast it as a colorless spell for its normal cost.
• WWizards of the Coast2022-10-14
  Official Ruling
  A prototype card is a colorless card in every zone except the stack or the battlefield, as well as while on the stack or the battlefield if not cast as a prototyped spell. Ignore its alternative characteristics in those cases. For example, while it's in your graveyard, Blitz Automaton is a colorless creature card with mana value 7. It can't be the target of Recommission, a spell that targets an artifact or creature card with mana value 3 or less in your graveyard.
• WWizards of the Coast2022-10-14
  Official Ruling
  If Hulking Metamorph somehow enters the battlefield at the same time as another permanent, Hulking Metamorph can't become a copy of that permanent. You may choose only a permanent that's already on the battlefield.
• WWizards of the Coast2022-10-14
  Official Ruling
  Use the appropriate printed power and toughness (either 7/7 or 3/3) to determine the result of Hulking Metamorph's copy effect.
• WWizards of the Coast2022-10-14
  Official Ruling
  You can choose not to copy anything. In that case, Hulking Metamorph simply enters the battlefield as a 7/7 (or 3/3) artifact creature.
• WWizards of the Coast2022-10-14
  Official Ruling
  If the chosen permanent is copying something else (for example, if the chosen permanent is a Clone), then your Hulking Metamorph enters the battlefield as whatever the chosen permanent copied, with the stated exceptions.
• WWizards of the Coast2022-10-14
  Official Ruling
  If the chosen permanent has in its mana cost, X is 0.
• WWizards of the Coast2022-10-14
  Official Ruling
  Except for also being an artifact creature and having a different power and toughness, Hulking Metamorph copies exactly what was printed on the original permanent and nothing more (unless that permanent is itself copying something or is a token; see below). It doesn't copy whether that permanent is tapped or untapped, whether it has any counters on it or Auras attached to it, or any noncopy effects that have changed its power, toughness, types, color, and so on.

Rulings via Scryfall