They scribbled down card names, effects, and quantities on index cards and, in some instances, even put strips of tape on playing cards to represent spells and creatures
Myr Retriever: a deterrent if someone wants to block it, and it they do and it dies, you can get one of your much better artifacts out of the graveyard
You can craft combos that you'd never be able to pull off in a mono-blue deck, but at that point all you've done is sculpted your own 2-color combo that you could've built into an actual 2-color deck anyway
Playset Value: Buy four cards for the price of three to maximize value and deck versatility
This is the mindset behind Pokemon TCGs Arceus set, which contains many unique and valuable printings of Arceus as well as its best creation, shiny Pokemon
This causes the cards to appear backwards upon opening the pack, reversing their reveal order and needing you to turn them over too