Pieces like Custodi Lich, Court of Ambition, Marchesas Decree, and Garrulous Sycophant are my favorites out of the available six
Hall and Oates
Kaust is a 2/2 Dryad Detective for just two mana (one green and one red/white hybrid, which can be paid with either color) that draws you a card when you deal combat damage to a player with a creature that was turned face up this turn
While it's certainly possible to get lucky and double your money with a box of Masters 25 even at current box prices, which are around $180$190if your goal is to build a Modern collection, you're probably better off spending your money on newly cheap Thalias, Eidolon of the Great Revels, Blood Moons, Utopia Sprawls, and the like
Tezzeret has ditched his black and blue colours and has gone completely colourless, with abilities just about any deck would want
The benefit of coven Coven itself is not an active ability, but a passive one