M Sableye & Tyranitar's GX attack on its own is ineffective, but also a strong win condition that your opponent MUST be aware of. Its normal attack is very VERY good. Umbreon EX saw a little bit of play, Guzzlord GX was interesting, but both of their attacks struggled because of their overall damage output. Buzzmosa GX saw heavy play in Japan for a month and its numbers worked out nicely due to its combination of two great attacks. Looking back in history, Plasma Lugia was extremely successful, and Rayquaza & Deoxys LEGEND saw play too. The prospect of taking three prizes on a Dedene, Lele, Koko, Blacephalon, UltraNecrozma, etc. is a threat. The prospect of taking FOUR prizes on a Pikarom with a choice band is a very nice perk. We have seen cards like this work in the past, and I believe Sabletar has similar potential.
In expanded, in combination with Weavile GX and acceleration, I believe this card has the potential to be an incredibly strong deck. Can't wait to see!