Assuming a "Galaxy Wizard" is under your control at the start of your Main Phase 1, and have a "Galaxy-Eyes Photon Dragon" on your Graveyard: activate the first effect of "Wizard" to make it Level 8, Normal Summon "Galaxy Knight" without Tributing, use its effect to Special Summon "Galaxy-Eyes" from the Graveyard and Xyz Summon this card.
If your opponent controls an Xyz Monster: Special Summon "Photon Slasher" with its own effect; then, activate "Galaxy Expedition" to Special Summon a "Galaxy-Eyes Photon Dragon" from the Deck. Special Summon another "Galaxy-Eyes" from your hand, by Tributing both "Slasher" and the first Dragon, Normal Summon "Galaxy Knight" without Tributing, triggering its effect and Special Summoning the Tributed "Galaxy-Eyes". Finally, Xyz Summon this card by using "Knight" and the 2 "Galaxy-Eyes".
And once your opponent controls an Xyz Monster, this card's effect will be able to use and detach all of that monster's Xyz Materials, giving this card a huge ATK boost.
If your "Galaxy-Eyes Photon Dragon" is targeted for an attack, activate the effect of "Galaxy Tyranno", then chain "Call of the Haunted" to Special Summon a Level 8 monster from the Graveyard; when "Tyranno" successfully Special Summon itself, use its effect and Xyz Summon this card.
Use "Accellight" to Summon a "Galaxy Wizard", then use "Inferno Reckless Summon" to bring 2 more "Wizards" to increase the level of all 3 "Wizards" by 4 and Xyz Summon this card. However, be careful to what your opponent could bring using "Inferno Reckless Summon".
If "Galaxy-Eyes Photon Dragon" is used as an Xyz Material, this card negates the effect of all face-up cards on the field. This is brilliant for the "Photon" archetype, as many of them have high ATKs but debilitating effects.
An OTK easily be makes with this card if your opponents have 2 or more Xyz Monsters on the field. Use this card's effect to detach all Xyz Materials from your opponent's monsters, and then use "Lightning Vortex".
To ensure an OTK it would be wise to use "Royal Decree" without using "Galaxy-Eyes Photon Dragon" as this card's Xyz Material. Another option would be to use "Trap Stun".