Monstrous is a designation that has no rules meaning other than to act as a marker that the monstrosity action and other spells and abilities can identify. Only permanents can be or become monstrous. Once a permanent becomes monstrous, it stays monstrous until it leaves the battlefield. Monstrous is neither an ability nor part of the permanent’s copiable values.
July 3, 2020 · Core Set 2021
Only two cards belonging to the same meld pair can be melded. Tokens, cards that aren’t meld cards, or meld cards that don’t form a meld pair can’t be melded.
August 23, 2019 · Commander 2019
A static ability may state that a creature “is goaded.” That creature attacks each combat if able and attacks a player other than the controller of the permanent with that static ability if able.
April 27, 2018 · Dominaria
rule 701.37b not present in this release
April 28, 2017 · Amonkhet
A permanent can be exerted even if it’s not tapped or has already been exerted in a turn. If you exert a permanent more than once before your next untap step, each effect causing it not to untap expires during the same untap step.