Properties of Beast Boost

Properties of Beast Boost:
Definition: When this Pokémon KOes another Pokémon through direct damage, its highest actual stat is boosted by one stage.
Property I: When the actual stats of the Beast Boost Pokémon are tied, the Beast Boost is prioritized in this order (in other words, there is no Beast Boost tie): Attack, then Defense, then Special Attack, then Special Defense, then Speed.
Property II: When a Beast Boost Pokémon takes a KO that would complete the battle, the Beast Boost is not shown to either player.

Notes: "BB" will be short for "Beast Boost" in the following.
Things like Speed Swap, Wonder Room, Power Split, etc. would modify the following certainties, but are not being considered for this list.

Naganadel:
-The maximum Special Attack of a Speed-BBing Naganadel is 179 stat (252 EVs, Timid)
-The maximum Speed of a Sp. Atk-BBing Naganadel is 179 stat (172 EVs, Timid)
-To get an Attack, Defense, or Special Defense BB, must have a boosting Nature and decreased IVs in Sp. Atk and Speed

Stakataka:
-Cannot ever get a Special Attack, Special Defense, or Speed BB
-The maximum Defense of an Attack BB-ing Stakataka is 201 (16-17 Def IVs, Lonely)
-The upper bound of Gyro Ball 150 BP for Attack-BBing Stakataka is 108 Speed (compared to 96 Speed with Brave)

Blacephalon:
-The maximum Special Attack of a Speed-BBing Blacephalon is 173 (12 Special Attack, Timid)
-The maximum Speed of an Attack or Sp. Atk-BBing Blacephalon is 174 (252 Speed, boosting Nature)
-Cannot ever get a Defense BB
-Can only get a Sp. Def BB with Careful Nature and decreased IVs in Attack and Sp. Atk

Nihilego:
-Cannot ever get an Attack or Defense Beast Boost
-The maximum Special Attack of a Speed-BBing Nihilego is 169 stat (172 EVs, Timid)
-The minimum Special Attack of a max Speed Sp.Atk-BBing Nihilego is 170 stat (180 EVs, Timid)

Buzzwole:
-Cannot ever get a Special Attack, Special Defense, or Speed Beast Boost
-A Defense-BBing Buzzwole cannot have more than 190 Attack stat (108 EVs, Adamant)
-An Attack BBing Buzzwole cannot have than 191 Defense stat (252 Defense EVs or 116 Def, Impish)

Pheromosa:
-Cannot ever get a Defense or Special Defense Beast Boost
-Cannot have more than 203 Speed (252 Speed EVs, neutral nature) and get an Attack or Special Attack BB
-If Pheromosa has a Speed-boosting Nature (e.g. Naive), it must get a Speed BB for the Speed-boosting Nature to actually give more Speed than 252 Speed EVs with a neutral-Speed Nature would give (this is basically another way to say the second point).

Xurkitree:
-Can only get a Special Attack BB

Celesteela:
-A Speed-BBing Celesteela cannot have more than 123 Attack, Defense, Special Attack, or Sp. Def

Kartana:
-Cannot ever get a Special Attack or Special Defense BB
-Can only get a Speed BB with a Timid Nature, 252 Speed EVs, and 21 or less Attack IVs
-Can only get a Defense BB with Impish Nature, 252 Defense EVs, and 0 Attack EVs

Guzzlord:
-Can only get a Speed BB with a Timid Nature, 252 Speed EVs, 19 Attack IVs, and 3 Special Attack IVs
-Can only get a Defense / Special Defense BB with a boosting Nature, 252 EVs, 17 Attack IVs, and 25 Special Attack IVs