Step 1. Normal Summon Neptabyss, using its effect to send Atlantean Dragoons to the GY and add Atlantean Dragoons to your Hand
Step 2. Use Atlantean Dragoons to add Mermail Abyssmegalo from Deck to hand.
Step 3. Summon Abyssteus by sending Dragoons from hand to GY, adding Mermail Abyssmander from Deck to hand and adding Moulinglacia from Deck to hand.
Step 4. Summon Abyssmegalo by sending Abyssmander and Fishborg Launcher from hand to GY
Step 5. Use Fishborg Launcher to summon itself and then use Launcher, Abyssmegalo and Neptabyss to Synchro summon Trishula, Ice Dragon of the Ice Barrier and use its effect.
Step 6. Summon Moulinglacia from hand and use its effect
Step 7. Activate Abyssmander's ffect and make Abyssteus level 9.
Step 8: XYZ Summon True King of All Calamities using Abyssteus and Trishula