Jirachi, Metagross AV (or Megagross, maybe a SpDef Zor if it exists) comes into mind. Tbh, I guess that you should run 216+ Speed on Jirachi to outspeed it because you definitely don't want to eat two hits from it.
Also, keep in mind that its Moonblast is significantly weaker than M-Garde, so the most important move to resist to is Psychic / Psyshock (and you try to stomach the others). I guess that things like Mandibuzz / A-Muk should work but do you really want to use those?
the problem i see in that, to resist psychic you use or another psychic (which will mean u will be doing jackshit to Lele), dark (who gets whiped with either fairy OR focus blast) or steel.
and in top of that, only those steels that dont take SE with Fblast will actually do something back.
what i want to say actually is that either you have a steel type NOT weak to Fblast or you are screwed...
and what about walls?
well, lets take suicune who is neutral to both stabs.
252 SpA Life Orb Adaptability Gardevoir Psyshock vs. 252 HP / 252+ Def Suicune: 148-177 (36.6 - 43.8%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
good¡ walls dont get 2KOed¡¡ yay
252 SpA Life Orb Adaptability Gardevoir Psychic vs. 252 HP / 4 SpD Suicune: 226-268 (55.9 - 66.3%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
or not...
and suicune is doing back...
0 SpA Suicune Scald vs. 0 HP / 0 SpD Gardevoir: 70-84 (24.9 - 29.8%) -- 1.2% chance to 3HKO after Stealth Rock
not much. and lele is faster anyway.
and since its stabs are only resisted by steel and Fblast is godlike, u can use dual psychic stab to wreck things that would wall you from whatever side of the spectrum.
Sand rush exca? if lele predicts the switch there ends the fun. and even if not a predict
252 SpA Life Orb Adaptability Gardevoir Psychic vs. 0 HP / 0 SpD Excadrill: 182-214 (50.4 - 59.2%) -- guaranteed 2HKO after Stealth Rock
cant come twice and needs the sand to revenge kill it properly
WAIT.
does psychic terrain stops pursuit in a changue? if it does so, then when u see Mgross u can just... switch out again like nothing happen.
252 SpA Life Orb Gardevoir Moonblast vs. 0 HP / 0 SpD Mega Metagross: 94-109 (31.2 - 36.2%) -- 99.8% chance to 3HKO after Stealth Rock
252 SpA Life Orb Adaptability Gardevoir Psychic vs. 0 HP / 0 SpD Mega Metagross: 58-70 (19.2 - 23.2%) -- guaranteed 5HKO after Stealth Rock
252 SpA Life Orb Gardevoir Focus Blast vs. 0 HP / 0 SpD Mega Metagross: 157-186 (52.1 - 61.7%) -- guaranteed 2HKO after Stealth Rock
and FB 2KOES Mgross. if pursuit is blocked by psychic terrain this pokemon is... basically imposible to revenge kill.