They can shut down a ton of your opponent's play, and with so few Main Deck Monsters, can run a ton of Hand Traps as well
Also great for decks that are running multiple lines of different type
Morselhoarder + Sinking Feeling + Power of Fire There are various ways to make this combo work, but Ill go over just one since the concept is pretty simple
Now that those Dragons are weak to Psychic Pokemon, Clefairy ex can dish out a potential total of 220 damage, assuming both players have full Benches each
Lurrus of the Dream-Den Companions break the game because players with companions start with a free extra resource, which gives them a huge edge over players without a companion
It also means that if you exile a creature and an artifact, then your artifact creatures will cost two less to cast