vs
Skill Drain
Card Text: Activate by paying 1000 Life Points. The effects of all face-up monsters on the field are negated while those monsters are face-up on the field (but their effects can still be activated).
Drytron Alpha Thuban
Card Text: Cannot be Normal Summoned/Set. Must be Special Summoned with the effect of a “Drytron” card. You can Tribute 1 other “Drytron” monster, or 1 Ritual Monster, from your hand or field; Special Summon this card from your hand or GY in Defense Position, then you can add 1 Ritual Monster from your Deck to your hand. You cannot Special Summon monsters, except monsters that cannot be Normal Summoned/Set, the turn you activate this effect. You can only use this effect of “Drytron Alpha Thuban” once per turn.
The Verdict
Case 1: Player-A controls a face up Skill Drain on the field, Player-B special summons Drytron Alpha Thuban (satisfying the conditions for the ritual monster search): Drytron Alpha Thuban will be able to resolve the search effect. Also the “You cannot Special Summon monsters…” effect is still in play.
WINNER = Drytron Alpha Thuban
Why: The effect of Drytron Alpha Thuban activates in the hand, Skill Drain has no effect on it. Therefore, the effect will resolve where it was activated (in the hand).
The reason the “You cannot Special Summon monsters…” effect is still in play, is due to this effect being a condition which applies the moment the first part of Drytron Alpha Thuban’s effect is activated.