Edison format ruling
Malevolent Mech - Goku En

Card effect (current official text)You can Normal Summon this card without Tributing. Once per turn, during the End Phase, if this card was Summoned this way: Send it to the GY, then take damage equal to its original ATK in the GY. This card must be the only Zombie monster on the field to activate and to resolve this effect.
Rulings
(U) You can Normal Summon this card without Tributing. (1) If you do, this card is sent to the GY during the End Phase if it is the only Zombie-Type monster on the field. When it is sent to the GY by this effect, you take damage equal to its ATK.
- The (U) Unclassified Effect does not activate, it applies in the hand.
- The (1) Trigger Effect is mandatory, it activates & resolves on the field in the End Phase.
- This effect ONLY activates & resolve is if it is the ONLY Zombie-Type monster on the field.
- This effect will activate during the End Phase of every turn (if this card was Normal Summoned with its [U] Unclassified Effect).
- If the activation of this effect is negated by Light and Darkness Dragon, it will activate again in the same End Phase [REF].
- If this effect resolves negated by Skill Drain, it will not activate again in the same End Phase [REF].
- This effect resolves without effect (Goku En is not destroyed) if an effect (like Call of the Haunted) is chained that Summons an another Zombie-Type monster to the field face-up.
- This effect resolves sequentially: first, send this card to the GY; then inflict effect damage.
- This effect inflicts damage equal to the original (printed) ATK of Malevolent Mech - Goku En.
- VS. Creature Swap: If this card (Normal Summoned by its [U] Unclassified Effect) changes control and activates its effect in the End Phase, the controller of Goku En on the field (when it was destroyed) takes the damage [REF1, REF2].
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Edison forum — sourced change requests get reviewed.