True Kings are definitely Level 9 monsters, but I've held back on putting them in the same Deck as Prediction Princess for some time because you really have no cards that benefit from being sent to the GY. People have historically played monsters like True King Agnimazud, the Vanisher and True King Lithosagym, the Disaster in Dinosaur because you could pop Babycerasaurus, Petiteranodon, and Miscellaneousaurus with the True King effects to get the Baby effects upon their destruction and Misc hits the GY where it can now banish itself for its effect. And it is also generally good to have Dinosaurs in GY to get something like a Souleating Oviraptor from Deck via Misc's effect from banishing 4 Dinosaurs from GY. Prediction Princess and general Ritual and Flip Support Monsters do not have much benefit, if any at all, from being in the GY or being sent to the GY. Yes, you could technically Ritual Summon your Prediction Princess Ritual Monsters from GY with Underworld Ritual of Prediction, but you still need to play monsters of a specific Attribute to use the effects of the True King monsters. The True King-related Attributes that we have access to the most are WIND and EARTH for Mariamne, the True Dracophoenix and True King Lithosagym, the Disaster respectively. For WIND, we have things like World Legacy Guardragon Mardark, Spirit of the Fall Wind, and handtraps like Droll & Lock Bird and Ghost Mourner & Moonlit Chill. For EARTH, we have things like Prediction Princess Bibliomuse, Deus-X Krawler, and Pot of the Forbidden. Even so, you don't really get much out of destroying these monsters and sending them to the GY, and besides, the True King you want to play the most of is True King Bahrastos, the Fathomer because of it being able to Special Summon a non-WATER Wyrm monster from Deck if destroyed by card effect. So in order to have some WATER monsters in Deck for a situation where I would need to destroy WATERs to Special Summon Bahrastos, I am playing Deep Sea Diva and Guitar Gurnards Duonigis which also provide a way to get to a Synchro Level 5 to get to Denglong, First of the Yang Zing who can modulate its Level to the Level of a Wyrm monster you send from Deck to GY by its effect. I still really don't recommend playing True King Prediction Princess as an actual Deck option. Because of the varying Attributes of your monsters and the fact that you don't really get much out of destoying your monsters via the True King effects, there is no realistic reason why you should even be considering something like this.
For the Main Deck monsters: 3 Prediction Princess Tarotrei and 1 Prediction Princess Tarotreith. Tarotrei can Quick Effect flip a monster face-up or face-down and can Special Summon a Flip Monster face-down during the End Phase from hand or GY. Tarotreith can either be Ritual Summoned or Special Summoned via Tarotrei's End Phase effect. It can Quick Effect flip any number of your monsters face-up or face-down and on flip, it can Special Summon a Flip Monster from Deck face-down. 3 Prediction Princess Bibliomuse. This card can Summon itself back face-down if it is Tributed and sent to the GY, and if it is flipped face-up, it can search for a Prediction Princess, other than itself, and a Ritual Spell from Deck. And while it is face-up on field, your Ritual Monsters gain targeting and destruction protection from your opponent's effects. 2 Deus-X Krawler which negates the activated effects of all monsters on your opponent’s side of the field after it has been flipped face-up and it can add a Level 9 monster with a different Type and Attribute than itself if it is destroyed on field. 1 Trias Hierarchia which can be sent off of Diviner or Special Summoned off of the effect of World Legacy Monstrosity targeting a True King on the field and Hierarchia can also Tribute a Fairy to Summon itself from hand or GY. For the True Kings: 1 True King Lithosagym, the Disaster, 3 True King Bahrastos, the Fathomer, and 1 Mariamne, the True Dracophoenix. Each True King needs to destroy 2 monsters from hand and/or your field, including at least 1 monster of their respective Attribute, in order to Special Summon themselves from hand. Lithosagym needs EARTH, Bahrastos needs WATER, and Mariamne needs WIND. Each also get an additional effect when you Summon them if you destroy 2 monsters of their required Attribute. Lithosagym allows you to look at your opponent's Extra Deck and banish up to 3 monsters from it with different names. Bahrastos can banish up to 2 Spell/Trap cards from your opponent's field and/or GY. Mariamne can banish up to 4 cards from the top of your opponent's Deck. Each also have an effect that activates if they are destroyed by a card effect: Lithosagym Special Summons a non-EARTH Wyrm monster from GY, Bahrastos Special Summons a non-WATER Wyrm monster from Deck, and Mariamne adds a non-WIND Wyrm monster from Deck to hand. Again, we are playing 3 copies of only Bahrastos because it is the most important one to destroy in order to get itseffect which allows you to Special Summon a non-WATER Wyrm monster from Deck. Say if you destroy Bahrastos and a Deus-X to Special Summon Lithosagym, Lithosagym is 1 Level 9 on field, and the destroyed Bahrastos Special Summons a Mariamne from Deck, giving you your 2nd Level 9 on field to go into a Rank 9. You could play 2 Lithosagym instead of 1 by cutting a copy of Gurnards, but I at least want to guarantee the Diva play in case I draw a Gurnards in my starting hand. Moving on, 2 Guitar Gurnards Duonigis which can banish cards from the top of your opponent's Deck equal to the number of WATER monsters you control if it is Special Summoned. This sets you up for a Deep Sea Prima Donna play, but I am not a fan of that card, so we can just use this effect as a way to scout out what your opponent is playing and maybe even banish an important card from their Deck. It can also target a Level 4 or lower WATER monster you control and increase its Level by its original Level. This goes very well when you get Gurnards off of Diva. By targeting itself, you have material for a Level 8 Synchro to go into White Aura Whale to destroy all Attack Position monsters your opponent controls going second, and if you target Diva, you have material for a Synchro Level 7 to go into Yazi, Evil of the Yang Zing which can pop itself and a card your opponent controls going second. And when it's destroyed by battle or a card effect, including by its own effect, you can Special Summon a Wyrm monster from Deck which can get you a True King to set you up for a potential Rank 9 play. 3 Deep Sea Diva which can Special Summon a Level 3 or lower Sea Serpent monster from Deck on Normal Summon. 3 Diviner of the Herald which can send a Fairy monster from Deck or Extra Deck to GY on Normal or Special Summon. And 3 Ash Blossom & Joyous Spring.
Spell/Traps: 1 Dragonic Diagram which can pop a card in hand or your field to add a True King or True Draco card from Deck to hand. 3 Underworld Ritual of Prediction which can Ritual Summon a Prediction Princess Ritual Monster from hand or GY face-up or face-down and you can banish it from GY during the Standby Phase to Special Summon a non-Ritual Prediction Princess monster from Deck face-down. 3 World Legacy Monstrosity which can either Special Summon 1 Level 9 monster from hand or target a Level 9 you control and Special Summon 2 Level 9 monsters with a different Type and Attribute than the targeted monster with different names. 1 Instant Fusion for Master of Ham. 3 Pot of Prosperity. 3 Infinite Impermanence.
Extra Deck: 1 Master of Ham which can Special Summon a Flip Monster from Deck face-down on Fusion Summon. 1 White Aura Whale which needs a Water Tuner and non-Water monsters for material which is easily fulfilled by Diva and Gurnards. On Synchro Summon, it can destroy all Attack Position monsters your opponent controls, and it can declare 2 attacks on your opponent's monsters each Battle Phase, also dealing piercing damage. And if it destroyed by your opponent's card by battle or effect, you can banish another WATER from GY to Special Summon it from GY as a Tuner. 1 Yazi, Evil of the Yang Zing which can target a Yang Zing you control and a card your opponent controls and destroy them, and if it is destroyed by battle or card effect and sent to GY, you can Special Summon a Wyrm monster from Deck. 1 Denglong, First of the Yang Zing which can search a Yang ZIng card on Synchro Summon, but we aren't playing anything searchable as nothing is that worthwhile to put in the Deck for Denglong to add, since you aren't always going into Denglong either way. It can also send a Wyrm monster from Deck to GY to change its Level to the Level of the sent monster. You can send a True King to make Denglong a Level 9 for Monstrosity and/or Rank 9 plays. 2 Herald of the Arc Light which adds a Ritual Monster or Ritual Spell if sent to GY. 1Divine Arsenal AA-ZEUS - Sky Thunder, 1 Infinitrack Earth Slicer, 2 Mereologic Aggregator, 1 Laevateinn, Generaider Boss of Shadows, and 1 Jormungandr, Generaider Boss of Eternity. 1 S:P Little Knight. 1 I:P Masquerena. 1 Gravity Controller.
Side Deck: 2 Nibiru, the Primal Being, 3 Thunder King, the Lightningstrike Kaiju, 2 Kashtira Fenrir, 2 Dark Ruler No More, 3 Evenly Matched, and 3 Solemn Judgment.
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