In an attempt to make Stage-1 and Stage-2 Pokmon more enticing to play, The Pokmon Company brought in the BREAK Evolution mechanic that allowed players to place a sideways card over a Basic, Stage-1 or Stage-2 Pokmon that would give it more HP and a new Ability or attack
If it is at full Sanity, and it enters with 3 Horror on it, on top of costing 4 Resources, meaning you need to spend a significant amount of money for an Ally that cannot tank anything on Carolyn, and once you do heal it to max Sanity, you still can't afford to let Foolishness take Horror, as that will remove the bonus
Destroy this card unless all 5 of these cards are in your GY, "Exodia the Forbidden One", "Right Arm of the Forbidden One", "Left Arm of the Forbidden One", "Right Leg of the Forbidden One" and "Left Leg of the Forbidden One"
You're likely to find them in a white commander deck, or modern white deck
In most competitive decks, Trainer cards are what make everything work