Super Starslayer TY-PHON - Sky Crisis — Ruling

Regola generale

About『During the turn, or turn after, your opponent Special Summoned 2 or more monsters from the Extra Deck, you can also Xyz Summon this card by using 1 monster you control with the highest ATK (your choice, if tied). (Transfer its materials to this card.)』:
This is not treated as an effect. It describes how you can Xyz Summon this card.
This method also is a proper way to Xyz Summon this card.
Similar to the regular procedure of using 2 Level 12 monsters as material to Xyz Summon this card, you can only Xyz Summon it using this method during your Main Phase. However, if you were to perform an Xyz Summon during another phase due to a card's effect, you can also Xyz Summon this card using this method.
If there are multiple monsters with the highest ATK you control, you can choose 1 to Xyz Summon this card using it as material.
Even if the monster with the highest ATK you control has an ATK of 0 (the only monster(s) you control have 0 ATK), you can use that monster as material to Xyz Summon this card.
If the monster with the highest ATK you control is a Token, you cannot Xyz Summon this card with this method. (It can also not be Xyz Summoned using another monster with the second highest ATK.)

About『If you do, you cannot Normal or Special Summon monsters for the rest of this turn.』:
This is not treated as an effect.
Even if you already Normal or Special Summoned previously during a turn, you can Special Summon this card with the method described.

About this card's ① st effect:
This effect is a Continuous Effect, which applies in the Monster Zone.
This effect applies to both players. (Even if there is a monster with 3000 or more ATK that is unaffected by monster effects, neither player can activate its effects.)