Legends is a very large set. For one, it is larger than Beta. It is also larger than the three other legal expansions in 93/94 combined (Arabian Nights, Antiquities, and The Dark). There is a handful of very powerful cards in the set; like Mana Drain, Mirror Universe and The Abyss, but there's also a vast amount of sub-par cards in there. Lets dive into some of the more infamous parts of Legends.
5. Mana Batteries
The Mana Batteries aren't as horrible as the other cards on the list here, it's just that their casting cost makes them utterly unplayable in every conceivable format. The cards would be actually good if they costed half as much to cast (two mana for these isn't an unreasonable wish either, they were printed between the moxen and Fellwar Stone). The development of Legends however had some issues, and to quote original playtester Skaff Elias:
"One huge factor that allowed the cardset to be completed on time was that, by-and-large, the Legends team didn't care about casting costs. If a card's effect was too powerful or out of flavor for the color, instead of trying to get an agreed upon alteration, or explaining concepts of color theme, we could just overcost the card by a mana or two -- a lot of this can be seen in Legends today."
The Mana Batteries ended up taking five uncommon slots in the set, and never being played in competitive decks.
Now we're getting somewhere! Five years ago, the BandsLands would have placed higher up on the list, but due to some more recent changes on the "Bands with other" rule, these lands are pretty close to having an actual effect these days. When printed, a card with e.g. bands with other Merfolk would, counter-intuitively, not band with other Merfolk. It would however band with e.g. a Zombie that had the ability Bands with other Merfolk. There were more strange subsections of this rule, but as even ordinary banding was kind of hard to understand a few years ago (and still is today), I wont go into to much details. Today, the cards actually makes your Legends able to form a band with other legendary creatures, and may at extremely rare and complex board states do something.
Glyph of Reincarnation is one of those cards that can make you appreciate the simple design of Raging River. Legends had a big Wall-theme, and I guess someone though that these would be excellent combat tricks. They are not. I can see you contemplating a situation where you donate a Wall of Dust to your opponent with Juxtapose, play a Creature Bond on it, attack with a random creature, play False Orders to make them block with the wall, and cast two Glyph of Destruction for the win. However, Glyph of Destruction can only target walls you control, so that deck isn't as good as you might think.
2. Landwalk hosers
This might be the actual worst cycle in Legends. Comparing this and the number one spot is a little like comparing them with Pikachu and Jack of Diamonds; you can't play either in Magic decks. I guess that Undertow is the one that have an even remote chance of having an effect, and that Great Wall is the worst offender here. No one ever even considered playing the "fixed" version of these cards, Staff of the Ages from Ice Age, and that is an artifact that stops all landwalk for 3 mana.
Dwarven Song. Haha. So you hear it, and become red for a while? I don't get it. Is it supposed to combo with Gauntlet of Might or Blue Elemental Blast? Were the laces from Alpha to powerful, and needed fixed versions? Mana Drain might be uncommon in Legends, but so is Sea King's Blessing :)
One more week until Christmas vacation btw. Looking forward to get back to Gothenburg for a while and play some old school magic over some sweet beer :)