Drytron Alpha Thuban

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.