What do the two Pokemon above have in common?

[Kakuna Matata]

Both have a 0 and an 8 in their respective National Dex numbers.

Gothita.

 

[MuddyMudkip]

Both can be encountered in B2W2.

Machop.

 

[Akromatic]

Both are sort of humanoid, and are loosely based on popular stereotypes: the bully/tough guy's kid and the goth girl.
EDIT: Damn. Forgot to post a Pokemon.
Um... Xerneas.

 

[NoirGrimoir]

Man, that one is hard, especially since we barely know anything about Xerneas. Well, both of their names contain an 'a'.

Dunsparce

 

[Bouffalant Herdier]

Both made their debut in an even-numbered gen.

Mareep

 

[KidBeano]

Both were introduced in Johto.

Mamoswine.

 

[Berrenta]

Both are from the Field egg group.

Beldum

 

[NoirGrimoir]

They can both be taught Iron Head through the Move Tutor.

Castform

 

[Bouffalant Herdier]

Both are gift Pokemon in Hoenn.

Sunflora

 

[Rainbow Cloud]

Both have abilities which are activated by sunny weather (not including Sunflora's DW ability).

Butterfree

 

[NoirGrimoir]

Both of their first evolutions can be caught at the National Park in Johto.

Sableye.

 

[Gaga]

They both have huge pretty eyes without visible pupils.

 

[Bouffalant Herdier]

I'm going to assume you meant to put Espeon's name at the end of your post.

~

Both can learn Shadow Ball.

Tropius

 

[Taco]

Both were in Pokémon Colosseum.

Larvitar

 

[Akromatic]

Both are considered Pokemon.
Helioptile.

 

[Berrenta]

Both are reptilian.

Leafeon.

 

[Akromatic]

Both have the letter E as the second letter in their name.
Fletchling.

 

[Kakuna Matata]

Both are obtainable at this time in XY.

Chinchou.

 

[Berrenta]

Both contain the "ch" sound.

Inkay

 

[Rainbow Cloud]

Both live underwater and are bioluminescent.

Dragonite