Beyond Gen II

This is my own note for how to prepare for future generations, based on two references: one and two.

Generation III (nothing to prepare for)

Babies (requires hatching):
Azurill (Marill baby)
Wynaut (Wobbuffet baby)

Non-babies (can be caught in wild):
Ralts> Kirlia > Gardevor (25, and 100 candies)
Nosepass
Roselia
Duskull > Dusclops (50 candies)
Chimecho
Snorunt > Glalie (50 candies)
Clamperl > Gorebyss (50 candies, evo item: deepseascale)
Clamperl > Huntail (50 candies, evo item: deepseatooth)
Feebas > Milotic (50 candies, evo item: prism scale, item introduced in Gen5?)

Generation IV (Need to save candies)

Babies (require hatching):
Happny (Chansey baby)
Mime Jr. (Mr. Mime baby)
Munchlax (Snorlax baby)
Bonsly (Sudowoodo baby)
Mantyke (Mantine baby)
Chingling (Chimecho (gen 3) baby) 

Evolutions from previous generation:
Magneton > Magnezone (100 candies, no evo item)
Lickitung > Likilicky (50 candies, evo item: rollout)
Rhydon > Rhyperior (100 candies, evo item: protector)
Tangela > Tangrowth (50 candies, evo item: ancient power)
Electabuzz > Electivire (50 candies, evo item: electrizer)
Magmar > Magmortar (50 candies, evo item: magmarizer)
Eevee > Leafeon (25 candies, evo item: moss rock)
Eevee > Glaceon (25 candies, evo item: ice rock)
Porygon2 > Porygon-Z (most likely 50 candies from Porygon instead of Porygon2 based on the past pattern, evo item: dubious disc)
Togetic > Togekiss (most likely 50 candies from Togepi instead of Togetic based on past pattern, evo item: shiny stone)
Aipom > Ambipom (50 candies, evo item: double hit)
Yanma > Yanmega (50 candies, evo item: ancient power)
Murkrow > honchkrow (50 candies, evo item: dusk stone)
Misdreavus > Mismaguis (50 candies, evo item: dusk stone)
Gilgar > Gliscor (50 candies, evo item: razor fang)
Sneasel > Weavile (50 candies, evo item: razor claw)
Piloswine > Mamoswine (most likely 100 candies from Swinub based on past pattern, evo item: ancient power)
Kirlia (Gen3) > Gallade (100 candies, evo item: dawn stone)
Nosepass (Gen3) > Probopass (50 candies)
Roselia (Gen3) > Roserade (100 candies, evo item: shiny stone)
Dusclops (Gen3) > Dusknoir (100 candies, evo item: reaper cloth)
Snorunt (Gen3) > Froslass (50 candies, evo item: dawn stone)

Generation V

Non-babies (can be caught in wild):
Cottonee > Whimsicott (50 candies, evo item: sun stone)
Lampent > Chandelure (50 candies, evo item: dusk stone)
Petilil > Lilligant (50 candies, evo item: sun stone)

Generation VI

Non-babies (can be caught in wild):
Helioptile > Heliolisk (50 candies, evo item: sun stone)
Doublade > Aegislash (50 candies, evo item: dusk stone)
Spritzee > Aromatisse (50 candies, evo item: sachet)
Swirlix > Slurpuff (50 candies, evo item: whipped dream)

Evolutions from previous generation:
Eevee > Sylveon (25 candies, evo item: affection, fair-type move?)

Generation VII

Evolutions from previous generation:
Pikachu > Raichu* (50 candies, a different Raichu, evo item: thunder stone)
Exeggcute > Exeggutor* (50 candies, a different Exeggutor, evo item: leaf stone)
Cubone > Marowak* (50 candies, a different Marowak, at night, no evo item)