Step 1. Activate Trade-in, Discarding Galaxy Eyes Photon Dragon and Drawing 2 cards (or get ashed, it doesn't matter)
Step 2. Activate Accelight, Special Summoning Galaxy Wizard
Step 3. Activate Galaxy Wizard's effect, tributing itself to add Galaxy Trance to the hand
Step 4. Activate Photon Sanctuary, summoning two Photon Tokens to the field
Step 5. Link Summon Galaxy Eyes Sol Flare Dragon using the tokens
Step 6. Activate Sol Flare's effect, adding Galaxy Wizard back to the hand
Step 7. Activate Galaxy Transfer, Paying 2000 Lifepoints and Special Summoning Galaxy Eyes from the graveyard, and also summoning Galaxy Eyes Afterglow Dragon from the deck
Step 8. XYZ Summon Number 90:Galaxy Eyes Photon Lord (if going first) or Number 62: Galaxy Eyes Prime Dragon (if going Second)

If you summoned Number 62:
Enter Battle Phase, and attack a card the opponent controls.
Activate Prime Photon's effect, detaching an Afterglow Dragon and increasing Prime Photon's attack by 1600
Activate Afterglow's effect, Special Summoning another Galaxy-Eyes Photon Dragon from the deck, and double Prime Photon's attack
Attack for a lot of damage