You can usually build 2 types of BLS decks: Decks that use Envoy of the Beginning in a Light/Dark themed deck or Bad Decks.
This Archetype is starving for decent support. No the Gaias don't count, I have desperatly tried to make them work, it ends in pain. No the new Fusion dosen't count either, That one was made for Dark Magician.
You could probably improve the deck (especially the extra deck) a bit more but this is what im rolling with mainly cuz i don't know any other good cards and also laziness.
Just get the Field Spell, Slam that sucker down, go for isolde, get Super Soldier Soul, send his *** to the GY, pop his GY effect to yoink a beginning or evening knight out of the deep dark pits of your deck, use the tokens on the Field Spell and then get the boi out there! Jarngreipr is there for protection if you are either going first, have 2 lvl 1 monsters or have bricked. Puppets cause GY setup into Kaiza and Kaiza cause more GY setup either through Super Soldier Soul or Kaiki for Gilti-Gearfried. Why am I using Vanilla BLS? Because Super Soldier ritual Sucks (in this deck at least). And also because on the off chance that you want to Ritual summon twice.
Why no Pre-Prep? You got 5 cards to get BLS and a Ritual Spell into your hands AND Pre-Prep only gets the vanilla Spell, not Synthesis (which btw lets u summon from the hand and GY, which is why Trade-in is there).
420
120
300
630
