On BST gap(originally intended to be posted on Serebiiforums)

[SPOILER=BST gaps lower than 151]
So far, the majority of BST updates have been on species with BST gaps lower than 160, to make them reach to 160. There are exceptions, of course, like Beartic and Magcargo which were updated to make them closer to Ursaring and Quagsire respectively, but for others are different matter, like, say, Dodrio, Electrode and Ariados.

[B]150:[/B]
Pawniard-Bisharp
Elgyem-Beheeyem
Koffing-Weezing
Stunky-Skuntank
Seel-Dewgong
Shellos-Gastrodon
Smoochum-Jynx
Krabby-Kingler
Mankey-Primeape
Meowth-Persian
Natu-Xatu
Snubbull-Granbull
Spinarak-Ariados
Sandshrew-Sandslash

[B]147:[/B]
Pancham-Pangoro

[B]145:[/B]
Trubbish-Garbodor
Venonat-Venomoth
Shieldon-Bastiodon
Cranidos-Rampardos
Wynaut-Wobbuffet

[B]142:[/B]
Glameow-Purugly

[B]140:[/B]
Vullaby-Mandibuzz
Anorith-Armaldo
Lileep-Cradily
Kabuto-Kabutops
Omanyte-Omastar
Tirtouga-Carracosta
Deerling-Sawsbuck
Cacnea-Cacturne
Spoink-Grumpig

[B]138:[/B]
Litleo-Pyroar

[B]130:[/B]
Meditite-Medicham
Goldeen-Seaking
Finneon-Lumineon
Chinchou-Lanturn

[B]125:[/B]
Ledyba-Ledian

[B]120:[/B]
Morelull-Shiinotic
Paras-Parasect

[B]115:[/B]
Mudbray-Mudsdale

[B]100:[/B]
Wailmer-Wailord
[/SPOILER]

Species below 138 bst gap besides Ledian are unlikely to get higher BSTs to their special statuses. The rest have counterparts that make this unlikely, such as Vullaby-line which is a counterpart to Rufflet-line, Arbok-Sandslash, the fossil Pokémon with each other etc. Leaving out these, we are left with a few choices, which are:

1. Elgyem-Beheeyem
2. Shellos-Gastrodon
3. Seel-Dewgong
4. Stunky-Skuntank
5. Koffing-Weezing
6. Spoink-Grumpig
7. Cacnea-Cacturne
8. Deerling-Sawsbuck
9. Venonat-Venomoth
10. Trubbish-Garbodor
11. Litleo-Pyroar
12. Pancham-Pangoro
13. Snubbull-Granbull
14. Pawniard-Bisharp

 155:
Numel-Camerupt
Carvanha-Sharpedo
Drowzee-Hypno

160:
Ekans-Arbok
Cutiefly-Ribombee
Voltorb-Electrode
Sandygast-Palossand
Snover-Abomasnow
Dwebble-Crustle
Salandit-Salazzle
Doduo-Dodrio
Corphish-Crawdaunt

165:
Shroomish-Breloom
Gulpin-Swalot
Buizel-Floatzel
Darumaka-Darmanitan

168:
Ducklett-Swanna

170:
Foongus-Amoonguss
Wingull-Pelipper

174:
Makuhita-Hariyama
Inkay-Malamar
Skrelp-Dragalge

175:
Pineco-Forretress

180:
Golett-Golurk
Snorunt-Glalie
Slugma-Magcargo
Yamask-Cofagrigus
Barboach-Whiscash
Electrike-Manectric
Remoraid-Octillery

185:
Surskit-Masquerain
Taillow-Swellow
Slowpoke-line

190:
Swablu-Altaria
Croagunk-Toxicroak
Mareanie-Toxapex