Not a combo, strictly speaking, but Mine addresses the biggest problem with Potion: its inflexibility. The Potion costs roughly the same as a Silver, but its non-fungibility imposes an additional premium. Drawing $7◉ is useless for getting a Province, while drawing $5, though ordinarily a good thing, can really set you back if you need to get in on the Familiars or Alchemists.
Mine helps alleviate this problem (provided Potions or Silvers are in hand) by allowing you to seamlessly transition between the two. Caught in an Alchemist race, but drew 3 Coppers + Silver + Mine? Mine your Silver into a Potion to get the Alchemist this turn. Played all five of your Alchemists, but your damn Potion is stuck at the bottom of your deck? Mine a Silver into a Potion so you can keep your chain going next turn. Late game, when your Potions are useless and you need all the buying power you can muster, you can Mine them into Golds (or better yet, Harems) for a significant money boost.
The biggest drawback to this is that there are other $5’s that may prove more important even in Alchemy games. (Mountebank, for instance, if Familiar is not present.) Mine is usually one of the weaker $5’s, but it is significantly bolstered by the presence of non-traditional Treasures. With Potion, it gets an added bonus of introducing flexibility into an otherwise risky investment. It’s worth picking up as part of a $5/$2, or if there’s no top-tier $5 otherwise.