No rocket cards, no base set 2 cards, no modern cards
Craft a unique background and story for your game, and then create various types of cards, like character cards, battle cards, and magic cards
If you run low on spare cards in YuGiOh Duel Master, chuck some Gems at the special bundles to get dozens of cards and earn a chance to get secret packs
1-2 Exhibition and Core (no 2-card combos) The community has determined this is a true 2-card combo
Thats not to say 5 mana for a Shrieker is cheap, but if you are trying to play a sped up game in a format with big dumb things and enters tapped lands, having effects that dont care about blockers late in the game is a plus
At the end of the Battle Phase, if your "Gladiator Beast" monster battled: You can shuffle that monster into the Deck or Extra Deck