As for Salazzle-GX/Garb, there's Field Blower to re-activate abilities after it knocks Garb's tool in the discard...
Meanwhile, Zoroark-GX(SHL) + Mallow(GRI) + Metagross-GX(BSH), + Max Elixir(Dusk Mane Necrozma is a basic)(BKP) + Altar of the Sunne(sorry, Newgaleo, but you're coming late to the party, and until you are released stateside, Altar of the Sunne will have to do as a weakness-negator)(GRI) + Lusamine(to recycle Altar of Sunne that are discarded in any way, whether field blower, other stadiums like scorched earth, brooklet hill, etc.)(CRI)= enough energy for the 1HKO, unless Glaceon-GX(which evolves from Eevee, whose Ability means Glaceon-GX can come into play T1 and since it has a EX+GX ability-negator that doesn't require a tool(but is only effective if it is in the active) and while it is in effect, wonder tags(Lele is a GX) are not possible, as the ability is negated by Freezing Stare) becomes a thing, if only for waterbox decks, in which case Solgaleo-GX can't protect the team from weakness(as he offers ability-based weakness immunity), as it is a Pokemon-GX. On the other hand, Leafeon-GX makes Newgaleo's ability insignificant against Fire decks that utilize the lurantis promo and Leafeon-GX(UPR, approx. set abbreviation, as the set is not officially released in the states yet) to trigger their evolution into Lurantis, meaning fire decks still have a way to get around Newgaleo, especially those that utilize Turtonator-GX and/or Ho-Oh-GX, which both can OHKO w/ a Choice Band attached(3 Lurantis in play), and/or a Belt(3-4 lurantis in play, depending on Turt/Ho-Oh) after Lurantis promo additions, regardless of Newgaleo/Altar presence. Shame that it has to come from a GX attack, but at least that means Hala will be more useful, especially after the time when Sycamore leaves standard(proj. next September).
^ In terms of Gardevoir-GX decks, I can see Leafeon-GX as a starter for GX attack alone, as that will be the play of the fire decks that could be otherwise left in uncertainty clouds post-Newgaleo, as w/ a 2 Turtonator-GX, 2-2 Leafeon-GX, 2-2 Alolan Marowak(recharge Turtonator after Bright Flame) and a 3-3 Lurantis promo build, after T1 Kiawe use, Choice Banded Turtonator-GX could become a Gardevoir-killer that's not affected by Infinity Force OR Newgaleo as much, as they would be both 1HKO'd w/ the sunny day+Band+Bright Flame combo, not to mention that the energy discards form Bright Flame hurt Infinity Force's damage...