Almost all the Plusle & Minun cards are related to each other, though. Some connected like the one you’ve shown, or like this partially overlapping one from POP3:
Sometimes they see each other in the artworks, like EX Deoxys for example:
or Dark Explorers:
And even if they don’t see each other or are connected, they are usually still related. Like the POP1 where both Plusle and Minun are inside the same dome glass house:
Or Legendary Treasures where Minun is cheering along with the winning side, and Plusle is sad with the losing side:
Here you can see all Plusle & Minun artworks, which you could place side by side: Plusle & Minun.
Not all are related unfortunately. And it seems to have stopped completely since Sun & Moon, since they are even different artists now 
Kinda a bummer, since I always like this theme that was going on with Plusle & Minun, and how both were made by the same illustrators and usually related to each other in terms of artwork.
Greetz,
Quuador