"What Lurks Beneath", known as "Decisive Battle! Spirit Tech Force" in the Japanese version, is the one hundred and twenty-eighth episode of the Yu-Gi-Oh! ARC-V anime. It aired in Japan on October 23, 2016 and in Canada on February 2, 2018. It became available with official subtitles via Crunchyroll on November 28, 2017.
Turn 3: Leo Leo activates two copies of "Spirit Reactor" ( 1) in his Pendulum Zones. He then activates the Pendulum Effect of his left "Reactor", letting him change its Pendulum Scale to that of another Pendulum Monster on the field. He targets "Timegazer" ("Reactor": 1 → 8). Leo Pendulum Summons "Spirit Tech Force - Pendulum Governor" (2800/2500) and "Spirit Gem - Salamander Core" (0/0) from his hand in Attack Position. Leo activates the effect of "Pendulum Governor", letting him Tribute a "Spirit Gem" monster that was Pendulum Summoned from the hand this turn that has not activated its effect to allow "Pendulum Governor" to use that card's effect up to twice this turn. He Tributes "Salamander Core". He activates the effect now, letting him destroy a monster on the field and inflict damage 800 to its controller. He destroys "Odd-Eyes" (Yuya: 4000 → 3200) and "Genghis" (Declan: 4000 → 3200). The effect of "Pendulum Governor" prevents any monsters besides Pendulum Monsters from targeting it for attacks. As Leo has cards in both of his Pendulum Zones, its effect also prevents monsters his opponent controls with Levels between those Pendulum Scales" from attacking "Pendulum Governor". Leo Sets a card.
Turn 4: Yuya
Yuya Pendulum Summons "Odd-Eyes" (2500/2000) from his Extra Deck and "Performapal U Go Golem" (1600/1000) from his hand, both in Attack Position. As it was Pendulum Summoned this turn, Yuya activates the effect of "U Go Golem", letting him Fusion Summon a Fusion Monster from his Extra Deck to using monsters he controls as the Fusion Materials, including "U Go Golem". He fuses "Odd-Eyes" with "U Go Golem" to Fusion Summon "Performapal Gatlinghoul" (2900/900) in Attack Position. As it was Fusion Summoned, its effect activates, inflicting 200 damage to Leo for each card on the field (Leo: 4000 → 1600). As "Gatlinghoul" was Fusion Summoned this turn using a Pendulum Monster as a Material, Yuya activates its other effect, letting him destroy a monster his opponent controls and inflict damage to his opponent equal to that monster's ATK. He targets "Pendulum Governor".