What Pokemon comes to mind for the Generation above?

[Red Knight]

Honchkrow.

Hisuian Samurott, if this counts.

Legends: Arceus is Gen 8, so yes, it counts.

A first stage Pokémon from Gen 9?

 

[Inland_Taipan]

Assuming first stage means not evolved, Nymble

Fully evolved 'mon from Gen 3

 

[Calvinッ]

Flygon

Any single / pure type pokemon from Gen VIII?

 

[Red Knight]

Hattrem. (Doesn't become Fairy type until it evolves into Hatterene.)

Single stage mon (no evolutions or pre-evolutions) from Gen 1?

 

[Rainbow Cloud]

Lapras

A Electric type pokémon from Gen V?

 

[Red Knight]

Emolga

Fire type from Gen 7?

 

[Inland_Taipan]

Blacephalon

Legendary/Mythical from Gen 4

 

[Red Knight]

Azelf

Fairy type from Gen 7?

 

[Inland_Taipan]

Primarina

Mega Evolution from Gen 6

 

[Calvinッ]

Mega Houndoom, the goodest boi

Any regional form (or regional evolution) from Gen 8?

 

[Inland_Taipan]

Obstagoon

Gigantamax form from Gen 8

 

[Red Knight]

Gigantamax Orbeetle

A Pokémon from Gen 1 with a Gigantamax form

 

[Inland_Taipan]

Kingler

Mega evolution introduced in Gen 9.

 

[Calvinッ]

Mega Falinks

Any final stage pokemon from Generation 2?

 

[Red Knight]

Slowking

A Grass type from Gen 2?

 

[Calvinッ]

Sunkern, the weak fella

A dual type from Generation 6?

 

[Inland_Taipan]

Diancie

Cross-gen evolution in Gen 4

 

[Red Knight]

Gliscor

A Gen 9 Pokémon with a signature Ability?

 

[GamingFan1997]

Gholdengo

A Psychic-type from Generation II?

 

[Red Knight]

Girafarig

A Ghost type from Gen 5?