Lightray Diabolos

"This card cannot be Normal Summoned. This card can be Special Summoned if there are 5 or more LIGHT monsters in your Graveyard" is not treated as an effect. It is a procedure to Special Summon a Special Summon Monster. (A Chain Link is not built when Special Summoning in this way.)

If this card was successfully Special Summoned from your hand by the method described in its text and was subsequently sent to the Graveyard, it can be Special Summoned from the Graveyard by the effect of "Monster Reborn".

The monster effect "Once per turn, you can banish 1 LIGHT monster from your Graveyard; target 1 Set card your opponent controls, look at it, and return it to the top or bottom of the owner's Deck" is an Ignition Effect. (This effect targets 1 Set card on your opponent's field. When activating this effect, you banish 1 LIGHT monster from your Graveyard as a cost.)

When resolving the monster effect "target 1 Set card your opponent controls, look at it, and return it to the top or bottom of the owner's Deck", you choose whether to return the card you looked at to the top or the bottom of the Deck at the time of effect resolution.