The static ability says "for as long as this card is encoded on that creature, that creature has 'whenever this creature deals combat damage to a player, you may copy the encoded card and you may cast the copy without paying its mana cost'" (Rule 702.99a)
A boost of three mana, or one mana on the turn you play the Monolith, is far too dangerous to be allowed to survive
You can obtain the Cutiefly (1-Diamond rarity) card by opening Celestial Guardians: Solgaleo from Celestial Guardians set
Still, all of these factors combine to ensure that the Terapagos ex is a particularly highly sought after card, and with its current average value sitting at an impressive $123 , it might be one you try and pull from boosters, rather than splashing out on the card on the secondary market
Even Standard is currently dealing with a cascade deck threatening the meta, abusing the way these mechanics interact with adventures