In the first set there are only 24 cards...20 Trainers and 4 stages...The trainers have 4 Pokémon each. Here's an example:

This Trainer has 4 Pokémon, A Ralts, A Sentret aswell as 2 Masked Out pokémon. Judging by their Sihlouettes...they appear to be Corphish and Togepi

You can use these cards after beating the game at the Card E Room in Fenasu City.

After you beat Each Virtual Trainer, it is Marked Down in a Log Book in the Card-E Room which lists the Difficulty and the trainers. You Also Earn PokéCoupons from this battle Now, each of these cards has 3 difficulty settings. Easy, Normal and Difficult and When you beat all 5 in the pack in a row a 6th comes along to battle you.

But, once you have beaten all 24 trainers in each difficulty, in a row (6 in Each Pack)...a real trainer arises and he has something that you can capture. You cannot move on to the next difficulty until you have beaten this trainer.

Beat Every Trainer with A Straight Win Across the Board, in all 4 Packs with the Easy Difficulty (Low Levelled Basic Evolution Pokémon) And a Trainer Comes that has a Dark Togepi
Beat Every Trainer with A Straight Win Across the Board, in all 4 Packs with the Normal Difficulty (Basic, Middle and some Evolved Pokémon) And a Trainer Comes that has a Dark Mareep
Beat Every Trainer with A Straight Win Across the Board, in all 4 Packs with the Difficult Difficulty (High Leveled Final Evolution Pokémon) And a Trainer Comes that has a Dark Scizor (Always Male)

In Essence, since Each Card can be battled in each difficulty including the 6th one...there is a whopping 72 Trainers in this pack which would seem to have 20.

Now the trainer cards are out of the way...the Stage cards provide a change in scenery for the Virtual Room which would normally just be a black room...in it you end up with the room changing to say the Stadium in Fenasu City as seen in the transformation below

Scans and Details of Each Card Will Come Soon.

Pictures Thanks to Pokémon Japan