Take a look at these examples to get a feeling of what different types of Special Cards there are, what image format is needed and what fits best for you.
Supporting Cards
...with Title + Effect to boost your Deck. Boosts should somehow represent youSupporting Mix Cards
...boost your Hand by using 5 of 10 available rows to use the higher Bone CountSupporting Logo Cards
...are fancy Business Cards for Brands, Events or Locations featuring their LogoCurse Cards
...aren't boosting your own hand but affecting your opponents to make them sufferPlayroom Cards
...affecting ALL Players and stay active until replaced or cleared by other Special Card Abilities