My attempt to make Rainbow Dragon playable (and, by extension, Crystal Beasts)

[Lonk]

Crystal Beast Garnet Bull

EARTH

Level 4

Beast/Effect

ATK 1900/DEF 1200

 

Each time a "Crystal Beast" monster is placed into your Spell & Trap Card Zone:  Draw 1 card.  If this face-up card is destroyed while it is in the Monster Card Zone, you can place it face-up in your Spell & Trap Card Zone as a Continuous Spell Card, instead of sending it to the Graveyard.

 

Crystal Beast Obsidian Crocodile

WATER

Level 4

Reptile/Effect

ATK 1000/DEF 2500

 

When this card inflicts battle damage to your opponent's Life Points:  You can Special Summon 1 "Crystal Beast" monster from your Deck or Graveyard.  Then, place this card in your Spell & Trap Card Zone.  If this face-up card is destroyed while it is in the Monster Card Zone, you can place it face-up in your Spell & Trap Card Zone as a Continuous Spell Card, instead of sending it to the Graveyard.

 

Crystal Beast Lapis Rooster

WIND

Level 4

Winged Beast/Effect

ATK 1200/DEF 800

 

When this card is Summoned:  Send 1 face-up "Crystal Beast" Continuous Spell Card to your Graveyard;  Special Summon 1 "Crystal Beast" monster from your hand.  If this face-up card is destroyed while it is in the Monster Card Zone, you can place it face-up in your Spell & Trap Card Zone as a Continuous Spell Card, instead of sending it to the Graveyard.

 

Crystal Beast Rainbow Chimera

LIGHT

Level 4

Beast/Effect

ATK 1700/DEF 1700

 

If this card battles:  You can send 1 "Crystal Beast" monster from your Deck to your Graveyard.  You can tribute this card and send 3 "Crystal Beast" Continuous Spell Cards to the Graveyard;  Special Summon 1 "Rainbow Dragon" from your hand or your Graveyard, ignoring its Summoning Condition.  If this face-up card is destroyed while it is in the Monster Card Zone, you can place it face-up in your Spell & Trap Card Zone as a Continuous Spell Card, instead of sending it to the Graveyard.

 

Crystal Beast - Purpose

Continuous Spell Card

 

When this card is activated:  You can add 1 "Rainbow Dragon" from your Deck to your hand.  Then, place 1 "Crystal Beast" monster from your Graveyard into your Spell & Trap Card Zone as a Continuous Spell Card.

 

Crystal Beast - Emotion

Continuous Spell Card

 

When a "Crystal Beast" card(s) would be sent to the Graveyard instead of being destroyed:  Send this face-up card to your Graveyard;  Place that card(s) from your Graveyard into your Spell & Trap Card Zone as Continuous Spell Cards.

 

Crystal Beast - Resolve

Continuous Spell Card

 

Activate only while there are at least 5 "Crystal Beast" monsters with different names.  Special Summon 1 "Rainbow Dragon" from your Graveyard, ignoring the Summoning Conditions and Trigger Conditions.  Then, Special Summon as many "Crystal Beast" monsters from your Graveyard as possible.  If "Rainbow Dragon" would be removed from the field by a card effect (including its own), you can shuffle this card into your Deck instead.