Check:

Diancie @ Leftovers
Ability: Clear Body
Tera Type: Ghost
EVs: 252 HP / 4 Atk / 252 Def
Careful Nature
- Stealth Rock
- Encore
- Diamond Storm
- Body Press
Diancie is a check to salamence. With a more physically defensive spread, diancie can always take two e-quakes and fire back with two diamond storms. If diancie gets a defense boost on diamond storm, it can definetely win. Diancie can also threaten salamence post tera with body press, with diamond storm+bp always ko'ing salamence. Encore can lock salamence into a move if needed, whether that be roost or draco meteor or e-quake to switch to an immunity. Stealth rocks can give diancie some merit even if salamence swaps out. Tera ghost can be a good neutral typing if salamence is potentially overwhelming diancie, so you can take a hit easier.
Calcs:
4 Atk Salamence Earthquake vs. 252 HP / 252 Def Diancie: 112-132 (36.8 - 43.4%) -- 98.8% chance to 3HKO after Leftovers recovery
4 Atk Diancie Diamond Storm vs. 0 HP / 0 Def Salamence: 260-308 (78.5 - 93%) -- guaranteed 2HKO
4 Atk Diancie Diamond Storm vs. 0 HP / 0 Def Tera Steel Salamence: 65-77 (19.6 - 23.2%) -- possible 5HKO
252 Def Diancie Body Press vs. 0 HP / 0 Def Tera Steel Salamence: 234-276 (70.6 - 83.3%) -- guaranteed 2HKO
Counter:

Bronzong @ Leftovers
Ability: Levitate
Tera Type: Water
EVs: 252 HP / 88 Def / 168 SpD
Bold Nature
IVs: 0 Atk
- Iron Defense
- Body Press
- Psychic
- Rest
Bronzong is a counter to salamence. With levitate and a steel typing, bronzong is either resistant or immune to every single attack salamence has on this set. From here, bronzong can do a few things. If your idea is to purely ko salamence as soon as possible, then psychic is a 3hit ko (unless you are unlucky). If you want to make salamence a set up opportunity (something which is hard to do reliably), then iron defense is here to boost the power of body press up to +6, which then is a 2hit ko. This also catches salamence post tera, as neutral bp is a guarenteed 2hit ko. Now, doesn't salamence just repeatedly chip down bronzong? Well, that's where rest comes in. Bronzong takes so little damge from salamence's hits, that being forced to rest against it is not really an issue, so its foolproof (unless you get unlucky with confusion procs and hitting yourself, in which case just go gamble at the casino, you will have better luck there).
Calcs:
252 SpA Salamence Hurricane vs. 252 HP / 168 SpD Bronzong: 61-72 (18 - 21.3%) -- possible 7HKO after Leftovers recovery
0 SpA Bronzong Psychic vs. 0 HP / 0- SpD Salamence: 108-127 (32.6 - 38.3%) -- 97.9% chance to 3HKO
+6 88+ Def Bronzong Body Press vs. 0 HP / 0 Def Salamence: 186-219 (56.1 - 66.1%) -- guaranteed 2HKO
88+ Def Bronzong Body Press vs. 0 HP / 0 Def Tera Steel Salamence: 188-222 (56.7 - 67%) -- guaranteed 2HKO