Welcome to the the Galactic World!

Galaxy-Eyes (or Galaxy Photon) is a deck used by Kite Tenjo in Yu-Gi-Oh! ZEXAL. The deck focuses on getting a bunch of Level 8 monsters on the field to XYZ summon powerful XYZ 8 that we'll see later, while being able to use XYZ 5 and 4 thanks to it's toolbox allowing it.

Skill

Galaxy-Eyes actually have 3 existing skills. As Xyz Galaxy and Galaxy Photon are not viable anymore, this guide will focus on Photon Dragon Advent .

Photon Dragon Advent is a very powerful addition to the deck, letting you add 2 monsters with different names,that are either Loading... or Level 8 Warrior-Type Galaxy monsters by revealing a Loading... or a Loading... . It's second effect (which is once per turn, not like the first effect which is once per duel) can set a Loading... from your deck or graveyard by discarding a Galaxy card from your hand.

Core cards:

Galaxy-Eyes Photon Dragon

Also known as GEPD, this card is the most important of the deck. it doesn't seem powerful as it only has an effect that is able to perform well in the battle phase, but many cards in the deck revolve around him and benefit more having at multiple copies that we'll see later. It also get to trigger the skill for it. 3 copies is the optimal way but if you can't afford a 3rd, 2 is playable.

Galaxy Knight
This card is the second most essential card of the deck, as it let you trigger the skill and can let you special summon Loading... from your graveyard if you normal summon it without tributing (by having a Photon or Galaxy Monster on the field). I personally prefer 2 copies as the duel will end way before a third one is useful, and having 5 cards that trigger the skill work for me but 3 is a great and logical choice.
Galaxy Brave

There is not too much to say about this card,it is an extender that you can special summon from the hand by revealing a Photon Monster, and you take the level of that revealed monster. Playing it at 1 copy is my recommendation, as it is usually played only once in a duel and Playing more copies could lead to some bricks.

Photon Vanisher
Photon Orbital

These 2 cards are a precious ressource for the deck. Photon Vanisher can be special summoned as long as you control a Galaxy or Photon Monster, and let you search a copy of GEPD. It is very useful as you can get your main monster of the deck, and can allow you to have some XYZ 4 plays with Loading... .

Photon Orbital is also a great ressource,you can equip it to a Photon Galaxy,and he gain 500 ATK and make the monste undestroyable in battle, synergizing with Loading... . It's second effect allow you to send him equipped to the graveyard to grab any Galaxy or Photon Monster, making him useful to get a monster you need in order to fix your hand.

Galaxy Soldier
Galaxy-Eyes Cloudragon

Galaxy Soldier can be special summoned by sending a light monster from the hand to the graveyard, and can get you an Galaxy Monster from the deck to the hand. This card will mainly be used as a starter in some combos route, and allow XYZ 5/Link plays. 2 Copies is playable but 3 is optimal to be comfortable with your hands.

For Cloudragon, it is a very important piece as you can benefit from it using the skill to set it and tribute it to special summon a Galaxy-Eyes monster from hand/graveyard.

Tech cards

Alright, now we'll talk about the staples. Before beginning to present what can be in the deck, note that Galaxy-Eyes is a deck that doesn't want too many tech cards in it's hand,otherwise you could brick too much because you have too much of them in your deck. Keep in mind that 4 staples is the great number, Or 5 if you really want it but 4 is really optimal for space. Note also that your staples choice will depend on the meta, as you really want to be able to have a massive advantage if you can drop that tech card.

Valuable Staples:
Forbidden Lance
Forbidden Chalice
Book of Moon
Effect Veiler
D.D. Crow
Artifact Lancea
Skull Meister
Book of Eclipse

I didn't want to include Loading... , as the card is a dead card turn 1 and isn't a top deck you want sometime,instead there are better techs that help you dismantle boards and protect/disrupt.

Archetype tech:
Hyper Galaxy
Photon Stream of Destruction
Galaxy Expedition

Honorable mention to them. They aren't necessary depending on your build or the meta but they definitely can enter your build to replace one pair of staples. Hyper Galaxy and Photon Stream of Destruction are both great disrupt,but i really recommend you to play Hyper Galaxy over Stream of Destruction as it give the deck a great disrupt by tributing 1 monster from both player's that have minimum 2000 ATK to special summon Loading... , which is great as it give the deck a key monster to avoid the lack of ressource to finish the game, which the deck really struggle with

Galaxy Expedition is really good,it let you special summon a level 5 or plus Galaxy or Photon monster from your deck as long as you control a level 5 or plus Galaxy or Photon. I higly recommend to play it in 1-2 copies maximum in the Loading... version of the deck.

Trade-In
Pot of Avarice