Random Card of the Day #83:
Library of Leng - 1
You have no maximum hand size.
If an effect causes you to discard a card, discard it, but you may put it on top of your library instead of into your graveyard.
This is probably what Spellbook should have been. Which is weird, considering that Library of Leng came first. To be honest I don't I've ever really encountered a problem that my "hand size was too big" in a game. Occasionally, yes--I will have eight cards in hand and have to discard one of them. But never have I had to discard more than once a game; these scenarios typically only happen early game when I play a Ravnica Bounce Land. And to include a card that makes you change your maximum hand size, it changes it from "which card should I discard?" to "I cast Library of Leng/Spellbook" instead of discarding it--and you may still have to discard if it's in your deck because that doesn't mean it's in your hand either. I would have much rather either kept my mana open for responses or discarded something useful, like a flashback spell or a big monster to Rise from the Grave later.
But yes, this is me hating on the former half of the card, essentially me hating on Spellbook. The real key component of this card is the latter saying. This now makes you "immune" to discard, and better yet, it's optional to put it on the library. So if your only card(s) in hand are lands, you can discard them to not "block" what you need off the top of your library. If your only cards in hand are spells, well you at least get to put them on the top of your library in the order you want, or better yet: mix and match what you toss out--flashbacks in the graveyards (maybe even Anger or any of his cycle) and put the card you needed on top of your library.
It's very versatile in the putting-on-top-of-your-library department, so its got its own little niche. It's clearly not going in every deck, but depending on the format, I suppose it couldn't hurt that bad having one in your sideboard. It could be useful if your opponent is playing Forced Fruition. I'm tempted to say 4/5 because it does quite a bit for 1 mana. But it's no Reliquary Tower and I don't know how often it would be relevant. 3/5