The McDonalds Pokmon cards might not sell for a lot on their own, but they can bring in a lot of profit when sold in large quantities
The most common way is the suspend mechanic, like on Search for Tomorrow or Sol Talisman, which lets you exile a card from your hand, put some time counters on it, and then cast the card for free when those counters are gone
It was also part of a vertical morph cycle in blue (Lumithread Field, Zoetic Cavern, Whetwheel) which all stayed in the file
In the above image, you can see an example of a Stage 1 Pokemon
Some cards act as very good support for Rat commander decks, enabling massive turns or turning your army of Rats into big threats that require immediate attention
A more recent version of monoblack control is Danish player Jimmi Kristiansen's sweet deck from n00bcon 6: Expect my visit when the darkness comes, The night I think is best for hiding all