The Gaffer Lifegain is already a popular theme among Commander decks, and The Gaffer easily slots into any of them
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of The Earth Crystal's first ability)
0: Create a 1/1 red Devil creature token with "When this token dies, it deals 1 damage to any target." 6: You get an emblem with "At the end of the first combat phase on your turn, untap target creature you control
Also, the decks I said it didnt belong to are a narrow band (with the main relevant one being Najeela, the Blade-Blossom)
Deharme All in all, card types are a broad topic with lots to discuss