They are very popular among collectors and players alike, not only for their functionality but also for their often unique design and collectible value
That means the front face must be a creature with a mana cost you can pay
Low Power Characters like 1-cost Belo Betty can become attackers, forcing the opposing player to play a Counter card to block the attack
It was great in the past, but being a level 5 that needs Normal Summoning and locks the player from attacking (outside of the monster they special summoned by its effect) makes it less useful these days
C Common Predaplant Bufolicula X DARK Level 1 [ PlantPendulumEffect ] ATK 0 DEF 0 P Scale 0 During your Main Phase: You can Fusion Summon 1 DARK Fusion Monster from your Extra Deck, using monsters from your hand or field as Fusion Material
This attack requires one Fire, one Psychic, one Dark and then two Colorless energy (thats any type of energy) to use