Notes & Combos
Essentially Fiendsmith Bystial handtrap control. The goal is to get to your Fiendsmith combo in a any way and back it up with impactful non-engine (which is why I opted for cards like Nib, Droll, Droplet, Super Poly... etc over low-impact handtraps like Veiler)
You have 15 1-card Fiendsmith combos in the deck, and the ability to get 2 bodies on the board with other means (a Bystial and any normal, super poly or nib and any normal) offsetting the card count.
50 cards for having a diverse non-engine setup and reducing the chance of bricking on duplicates, because it's really important for all cards in your hand to be usable in this deck. Going second doesn't feel as oppressive with this deck.
Neo Space Connector is the best Fiendsmith normal summon for this concept because it immediately demands a response, otherwise they will lose their Ash, freeing up your other plays that lead you to Fiendsmith anyway if you can put one more monster on the board. And with Millennium monsters high ATK, you can even snipe the Bystials or combo starters twice (by linking a Millennium with Dolphin then bring it back) from your opponent's hand.
You could also simply run 3 Tract 3 Lacrima.