Therion "King" Regulus

Per-phrase breakdown

• You can only use each of the following effects of "Therion "King" Regulus" once per turn. (Condition)
• You can target 1 "Therion" monster or 1 Machine monster in your GY; Special Summon this card from your hand, and if you do, equip that monster to this card. (Ignition)
• When your opponent activates a card or effect (Quick Effect): You can send 1 "Therion" Monster Card from your hand or face-up field to the GY; negate that effect (Quick)
• A "Therion" monster equipped with this card gains 700 ATK, also it can activate the 2nd effect listed above as if it were "Therion "King" Regulus". (Continuous-like)

Judge-facing facts

• Normal Summon / Set from hand uses 2 tributes (Level 8).
• You can only use the Special Summon effect and the negation effect once per turn each.
• The Special Summon effect is an Ignition Effect activated in the hand that targets 1 "Therion" or Machine monster in the GY.
• Special Summoning this card and equipping the targeted monster occur simultaneously at resolution.
• If the targeted monster leaves the GY before resolution, this card is still Special Summoned from the hand, but nothing is equipped.
• The negation effect is a Quick Effect that activates in the Monster Zone directly in chain to the opponent's activation. It cannot be activated during the Damage Step.
• Sending 1 "Therion" Monster Card from the hand or face-up field to the GY is the cost for the negation effect. A "Therion" Monster Card in the Spell & Trap Zone can be sent as this cost.
• The effect granting ATK and the Quick Effect to the equipped monster does not start a Chain Link and is treated as the effect of an Equip Spell Card.

Card-specific notes from database

• Cannot activate the Quick Effect if a 'cards sent to the GY are banished instead' effect is applying, as the cost cannot be paid (YGOResources).
• If this card's effects are negated, any monster equipped to it by its own effect is destroyed, and this card loses the gained ATK and effects (YGOResources).
• If a monster is equipped to this card by a different card's effect (e.g., 'Therion Stand Up!'), that equipped monster is not destroyed if this card's effects are negated (YGOResources).
• If multiple monsters gain the negation effect of 'Therion "King" Regulus', that gained effect can still only be used once per turn globally across all copies and gained instances (YGOResources).
• If a 'Therion' monster activates an effect gained from an equipped 'Therion' Monster Card, it is treated as a monster effect activated by the equipped monster in the Monster Zone, not as a Spell effect (YGOResources).
• If the Special Summon effect resolves while 'Skill Drain' is applying, this card is Special Summoned and equips the target, but the equipped monster is immediately destroyed because the effect to maintain the equip is negated (Konami neuron).
• If 'Crossout Designator' is applying to 'Therion "King" Regulus', a monster equipped with it can still activate the gained effect, because the activated effect belongs to the equipped monster (YGOResources).