>>48135498My first recommendations to anyone that wants to get into card investing is to hoard sealed product. It doesn't matter what: booster packs, booster boxes, ETBs, sealed cases, tins. Just pick product within your price range and put them in your closet for a couple years to mature. Look at any product from the Black and White era or early XY- those prices will be seen with Sun & Moon and Sword & Shield in the future, even "shitty" sets like Crimson Invasion. Look for good deals on these products while they're still cheap and watch your ROI grow.
As far as single go:
Keep your eyes on Special Delivery Bidoof. Due to the release being an absolute gong show a lot of people missed out on getting this card. Now that the release is done there will be no additional cards on the market barring a second release next Bidoof Day which I think will be unlikely. If I had a ton of cash right now I would probably try to buy up ever SDB on the market to control the price. Also be ready for Special Delivery Charizard's release.
I think the Japan Post cards are another set of promos that have a lot of growth ahead of them. Their release is also strange and barred NA buyers from getting ahold of them outside of knowing someone who physically lives in Japan. They did state there would be additional reprints, but I'm skeptical about the volume, and the market will probably absorb them anyway. I believe the release is in October so I'm waiting to see how the market changes when people get the physical cards in hand.