LogFAQs > #972449551

Because having one overpowered button is all you need.

That's a glib answer so let me rephrase it a bit: Darknite's balancing mechanism IS that some of its abilities are OP and he has a lot of them. Here's an excerpt of the math we did when mapping out Darknite effects, just so you can see the percentages at play:

-Darknite has 41 cards in the deck.
-Of these, six do nothing on their own (the four pieces of Exodia if you don't have the head, Saggi the Dark Clown, Trent). Percentage of nothing happening on your draw: 14%.
-Three abilities (Baby Dragon, Pot of Greed, Sangan) are fetches. You pay AP to do nothing to win this match this week (unless you incur fatigue and pay MORE AP, which, fair tbqh). Percentage of no effect including fetches: 22%
-One is Exodia. You need four of the above bad draws to use it at all. Percentage of no effect including Exodia if you don't have the pieces: 24%
-Four cards (Summoned Skull, Gaia the Fierce Knight, Flame Swordsman, Cocoon of Evolution) have fairly weak effects, from 'has horse' to 'is on fire', or have a good effect you never wanna use if your match is contested instead of having been beaten hard already. Percentage of no or minor effect draw: 34%
-Seven cards (Fortress Whale, Dark Magician #2, Dark Magician Girl, Crush Card Virus, Insect Queen, Mask of Brutality, Twin-Headed Thunder Dragon) have moderately good effects that can have good upside if you either get lucky, have the right team setup for it, or in the case of Crush Card Virus, drew a useless card to make it happen. Percentage of no, minor or moderate effect: 51%.

I could go into the upper tiers of Darknite's power and start breaking down exactly what the chances are of getting a given type of effect, but hopefully this makes the point. Over half the time, you'll draw something that either does nothing, does a minor thing, does something useful but doesn't help you win the match significantly, or does something genuinely good but it requires either a won terrain bid, the right kind of team, luck or setup to get value out of. Meanwhile, Len can target a merc you need disabled, guarantee get rid of them (unless they are good bakers I guess, but that's a very small amount of mercenaries), and you can't even juke it by not rostering the target because it'll go onto someone else, thus guaranteeing you'll always get some kind of value out of her. We rate consistency and reliability extremely highly, and Darknite doesn't have that once you axe Heart of the Cards repicks.

Sans is another story because his base abilities mostly kinda suck and are jokes, so he's reliable but is an EXP sink, and you can never reuse the good shit save a couple defensive moves. We may adjust him, but it's a case where we have to consider just how valuable he is when players are gaining half the EXP they did in the TR per match, because that changes the pace of ability acquisition dramatically.

EDIT: We could put a Recharge on Heart of the Cards, FWIW, and err on the side of safety. That is certainly something we could do. We'll see if that's a necessary nerf to make it fair on top of 'can't draw the thing twice' or not.