Monsters - 17
2 Dragon Queen of Tragic Endings
2 Malefic Cyber End Dragon

3 Crystal Beast Sapphire Pegasus
3 Crystal Beast Amber Mammoth
3 Crystal Beast Ruby Carbuncle
3 Crystal Beast Topaz Tiger
1 Summoner Monk

Spells - 22
2 Ancient City - Rainbow Ruins
3 Crystal Beacon
2 Crystal Blessing
2 Crystal Promise
3 Rare Value
1 Dark Hole
2 Lightning Vortex
1 Monster Reborn
2 Pot of Duality
2 Terraforming

Traps - 1
1 Treacherous Trap Hole

Extra Deck includes:
3 Cyber End Dragon
*other extra deck staples*

When crystal beasts are destroyed, you can send them to the s/t zone as a continuous spell. This deck aims to take advantage of that. What better way to do that than with the archetype's own field spell, Ancient City - Rainbow Ruins, which gains effects based on the number of crystal beasts in your backrow.

Sapphire Pegasus is going to be your main monster here. When he's summoned, you get to search your deck, hand, or graveyard for a crystal beast and put it into your s/t zone. Crystal Beacon is another key card for this engine, special summoning another crystal beast from your deck (usually Pegasus). Rare Value and Ancient City add a lot of draw power to the deck. If that wasn't enough power, we've got Dragon Queen of Tragic Endings to draw more, make our opponent discard, and can revive itself from the graveyard at the cost of 1 continuous spell. Once this deck gets going, you can have a lot of cards in your hand. Lightning Vortex is here

One of the biggest weaknesses of crystal beasts is their lack of firepower. Rainbow Dragon forces you to use the "less desirable" crystal beasts, and requires a degree of setup. You usually want Pegasus to be fetching you either more Pegasus for Crystal Promise, or Carbuncle to set up a cyrstal beast spam later on. Hamon is another popular choice for a beatstick, and while he is easy to summon with this deck, he doesn't have a lot of synergy with the other cards. Hamon sucks up 3 of your continuous spells, which will hurt all the other cards of the deck. It wrecks your use of Rainbow Ruins, Beacon, and Rare Value.

So, how else can you make up for crystal beasts low attack power? Enter Malefic Cyber End Dragon. It costs you literally nothing to special summon this 4000 attack beatstick. You need to keep a field spell in play, but that should be easy because Rainbow Ruins can't be destroyed as long as you have 1 crystal beast in your s/t zone. But it gets better. With Rainbow Ruins and 3 beasts in the s/t zone, you can tribute your beasts to rainbow ruins to protect your Malefic monster from your opponent's spells and traps.