Neiroy, the Dream Mirror Disciple — Ruling

Effetto 1

This card's effect that Special Summons itself is an Ignition Effect that activates in your hand. (It does not target. It can be activated optionally if a "Dream Mirror" monster is on your or your opponent's field.)
When resolving this effect, you will first Special Summon itself, and afterwards you can make its Attribute become DARK. (Both parts are are not treated as happening simultaneously.)

This card's second effect is a Trigger Effect that activates on the field. (It does not target. It will also be activated during the Damage Step. It is mandatory to activate, even if neither Dream Mirror of Joy nor Dream Mirror of Terror is on the field.)
If Dream Mirror of Joy is on the field when resolving this effect, you can return 1 Spell/Trap your opponent controls to the hand. If Dream Mirror of Terror is on the field, draw 1 card, then shuffle 1 card from your hand into the Deck. If both cards are on the field, both effects can be applied.