If youre just starting, a recent, well-reviewed precon is a great launchpad
Its a big list, no doubt, and Im sure Ive not included half as many cards as I should have
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Karmic Guide, Mulldrifter, Elvish Mystic, just to cite a few
Others introduce elements to the game that increase the pace or intensity of the game, making it more interesting
For example, I recently built a version of Aang, at the Crossroads, where the entire game plan was to resolve it and then copy it repeatedly to keep retriggering its ETB ability