S rank
Groudon-Primal (Red Orb) - Depends on defensive investment.
Zygarde (Lucarionite, Altarianite, Pinsirite) - Can't realistically trap.
A rank
A+:
Magearna (Cameruptite, Sablenite, Blue Orb) - Cam doesn't die until at 90% - beware of OTR + CM, as one wrong move may put you in the dust. Also be wary of Pinsirite flying overhead. Defensive variants need Fleur Cannon stalled out, but any other variant works fine
Terrakion (Lucarionite, Diancite) - Guaranteed to eliminate Lucarionite.
A:
Blissey (Sablenite) - Guaranteed to eliminate.
Buzzwole (Aggronite) - Cannot eliminate reliably.
Entei (Altarianite, Pinsirite) - Cannot eliminate period.
Mew (Sablenite, Aggronite) - Aggronite is extremely difficult to trap - EQ doesn't always do half damage, and U-turn is a very possible move if you're attempting to Substitute stall out to get into Reversal range...
Kartana (Metagrossite) - Guaranteed RK if Dugtrio is chipped into 100 BP Reversal (or more)
Victini (Red Orb) - Near enough a guaranteed trap.
A-:
Arceus-Fairy (Pixie Plate) - Can't really trap this one.
Arceus-Ghost (Spooky Plate)
Gliscor (Venusaurite)
Golisopod (Blue Orb) - No.
Ho-oh (Life Orb, Leftovers, Choice Band)
Landorus-Therian (Salamencite, Altarianite)
Lunala (Lunalium Z, Choice Specs)
Necrozma-Dusk-Mane (Solganium Z) - DM is nearly KO'd by 200 BP Reversal.
Necrozma-Ultra (Ultranecronium Z) - Chipped at 59% or lower, Ultra is reliably removed.
Shaymin-Sky (Diancite, Red Orb)
Toxapex (Gyaradosite, Latiasite) - One of the more important traps. Needs to bring up a Substitute vs Gyaradosite and mega to KO, however
B rank
B+:
Keldeo (Lucarionite, Diancite) - KO at 55%.
Metagross (Pinsirite)
Shuckle (Gyaradosite, Ampharosite) - Lets hazards up but can force its own SR up and a Substitute
Skarmory (Blue Orb, Venusaurite)
Tapu Lele (Diancite, Lucarionite) - This one is a particularly important removal for stall-based teams. 72.5% gives a guaranteed KO.
Volcarona (Red Orb, Cameruptite) - Not really something that can be trapped, however +1 Cameruptite is lured by Stone Edge Dugtrio, and 70.4% Red Orb is KO'd on a double
Xerneas (Power Herb, Choice Scarf, Fairium Z) - Xern isn't something that will go down easily, nor is it trappable at +2.
Zapdos (Sablenite, Venusaurite, Manectite)
B:
Arceus-Ground (Earth Plate, Groundium Z) - 252 Atk Dugtrio Reversal (200 BP) vs. 252 HP / 132+ Def Arceus-Ground: 265-313 (59.6 - 70.4%) -- guaranteed 2HKO. Trap at your own risk.
Azelf (Red Orb) - Guaranteed trap (even unmega!)
Cobalion (Pinsirite, Diancite)
Kyogre-Primal (Blue Orb) - Depends on EVs (again). Reversal can OHKO 252/0
Manaphy (Absolite, Cameruptite) - Reversal OHKOs, EQ does 56 min
Raikou (Red Orb) - Guaranteed trap!
Salamence (Salamencite)
Weavile (Glalitite, Lucarionite) - Priority prevents from being trapped
Zygarde-Complete (Leftovers, Groundium Z) - Usually too bulky to be reliably trapped.
B-:
Arceus-Dragon (Draco Plate) - Alike to Groundceus...
Arceus-Flying (Sky Plate)
Arceus-Water (Splash Plate) - Ceus calc.
Arceus-Rock (Stone Plate) - OHKO'd by Reversal. Usually reliably trapped on a double.
Darkrai (Diancite, Blastoisinite) - Blastrai is OHKO'd by Reversal. Deals ~56 min.
Ditto (Choice Scarf)
Excadrill (Lucarionite, Pinsirite) - Reliable OHKO, but not in non-mega form
Genesect (Altarianite, Pinsirite) - Revenged by priority.
Giratina (Leftovers)
Giratina-Origin (Griseous Orb)
Hippowdon (Venusaurite, Sablenite) - Very difficult to trap.
Jirachi (Ampharosite) - OHKO'd by Reversal, EQ requires some chip (~20%)
Rayquaza (Life Orb)
Tapu Koko (Diancite, Lucarionite) - Neither variant is trapped due to Speed.
C rank
Arceus (Normalium Z) - Priority revenges.
Archeops (Diancite)
Celebi (Blue Orb)
Gastrodon (Manectite, Sablenite) - Reversal KOs at 70%.
Mamoswine (Lucarionite) - Ice Shard revenges.
Stakataka (Heracronite) - TR prevents trap, usually