For the uninitiated, and I gather that most players don't have much experience with Vintage Storm decks, the application of Necropotence in Vintage combo decks is different from its historical use in most of the decks I've talked about here. While there's no exact rule, old Necro decks tended to be built so that the right move was to overpay on Necropotence activations such that you'd have 8 or 9 cards in hand, but it might be more when facing decks that couldn't put pressure on your life total. You'll have to discard down to 7, but even setting up a hand of 10 or 11 cards could work, ditching extra lands and the cards that are least suitable for the matchup, building a strong hand for the next turn. Going too much higher just meant you were throwing a lot of cards (and life) away to dig for specific tools, and those decks tended to be sufficiently consistent that such digging wasn't usually necessary. Vintage Storm decks use lots of restricted cards, so they cannot be as consistent. In these decks, the idea is to balance the threat the opponent presents to your life total against your own deck's potential to get enough mana and card-drawing to lead to a probable next-turn kill. Similar to Type 1 Necro-Donate before the restriction of Necropotence, you're probably expecting to only have one or two turns of activating the card before the game is over. Several restricted cards can have a high impact after being acquired by Necropotence in a game. But the possible outcomes are numerous. The most powerful tool is probably Yawgmoth's Will, which can reuse Rituals and other cheap cards to ensure a lethal storm count for Tendrils of Agony. The right number of times to activate Necropotence could vary from deck to deck, especially as the archetype evolved over the years. But in general, it'd been advisable to go for bigger hands, often setting up a hand of 12 cards or more. I've had games where I was shooting for 15 cards after a first-turn Necropotence (that's not paying 15 life, because a first-turn land, Ritual, Necro play leaves 4 cards in hand already, so it's paying 11 life, and most opponents are going to need a couple of turns to do 9 more damage to me). With so many single-slot cards making such a big difference in gameplay, I find using Necropotence in a Storm deck to be kind of annoying, even though the card is a favorite of mine and the archetype is also a favorite of mine. Kills that rely on Necropotence are some of my least favorite lines to take in Vintage Storm decks, but there are simply too many other cards restricted for a Storm deck to have the consistency to do without Necropotence. It's a deck slot I take with grudging acceptance. The card is simply too powerful not to use.