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 Spell 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 Zeta Aldhibah once per turn.