Cards that don't function within MTG's rules, but "are intuitive, and otherwise non-problematic"
Cumulative upkeep says, "Hey, pay 3." Echo says, "I'm still good." And fading says, "Take off my last fading counter." Turn #8 During your untap step before you untap, Old Fogey phases out
Omnath, Locus of All can draw ultimatums faster and give you extra mana, and General Ferrous Rokiric gives you a big golem
Design like this I especially like
A counterspell for noncreatures at two mana that also prevents your opponents from casting noncreature spells for the rest of the turn feels pretty powerful, even though its not without its limitations
If you do, draw X cards, then put up to X land cards from your hand onto the battlefield tapped, where X is the sacrificed creatures power. Being able to throw away some of your cards for not just extra cards in your hand but also extra land in play is game-winning