You can put Fiendsmith into everything. Even in Earth Machine (Yugioh Combo w/ MIT ft Fiendsmith)

btw , when beatrice gets banned , this will not work no more
2 copies of Fiendsmith are fine. You don't need the extra fiendsmith cands for the Extra deck
**UPDATE**
After September 2 2024 , beatrice got banned , so this line doen't work anymore. If another got rank 6 for Earth Machines comes out , then you can summon that instead