The world cycle

Darkside Serpent
*8 DARK Sea-serpent/Effect 0/3200
Cannot be normal summoned or set. You can special summon this card if you control a level 8 monster. You can tribute this card if you control another level 8 monster to destroy 1 card on the field.

Stardust Serpent
*8 LIGHT Sea-Serpent/Effect 1600/1600
Cannot be Normal Summoned or set. When a level 8 monster is removed from the field, you can special summon this card in ATK position. You can discard 1 card to banish 1 level 8 monster from your deck. Special summon it during your next standby phase. This effect applies even if this card is no longer face-up on the field

Eternal Dualistic Cycle
Continuous Spell Card
Once per turn, you can tribute 1 level 8 monster to special summon 1 level 8 monster from your deck with a different attribute and lower than 2000 ATK. When the monster summoned by this card is destroyed, special summon the monster tributed by this card from the graveyard or banished pile.

Dualism of Law and Chaos, Ouroboros
Rank 8 Sea-serpent/Effect WATER 2400/2400
1 Dark level 8 monster + 1 LIGHT level 8 monster
This card is also treated as an EARTH monster. Can only be Xyz summoned. You can banish 2 cards with the same card type from your graveyard  to activate the effect of 1 card in your hand with the same card type during either player's turn. If you do, discard it. You can detach 1 Xyz material from this card and return 3 of your banished cards to the graveyard to negate a card effect that would remove this card from the field and destroy it.