Promo Cards are also generally (but not always) marked by a stamp of some sort on the right side of the image, as seen on the picture of Mankey above
Several of these spells care about the number of Lessons in your graveyard, which turns the discard on Black-Green +1/+1 Counters Arm your creatures with +1/+1 counters through a variety of means
Selesnya is great at making big board states and less good at recovering from board wipes or giving evasion, and thats magnified in a card pool without Craterhoof Behemoth
The key lies in older, rarer, out-of-print cards you wont find in bulk on eBay and gem mint cards worthy of a display case
Mewtwo from 151 Ultra Premium Collection Extended Art DOES NOT INCLUDE CARD
For example, you can't sacrifice one creature card out of a merged creature if you're instructed to sacrifice a creature