The March Hare's ability has some Fridge Horror to go with it. It may save your life by making your enemies think you're dead, but who knows what things will be like when you wake up? You could have been hurt worse and know you really are dying now, all of your friends/family could have been killed and your home destroyed, or you could even wake up in a coffin and have no way out.
Every chain with the exception of Oz and Cheshire was actually once a human. Meaning the things our heroes have been killing left and right were- or if they retain their consciousness, are- people just like them.
Everything about the Bakservilles and Child of Misfortunes were lies as the Jurors only used the former for their stories and feared the latter for being created by the Core of the Abyss on a whim and because of their able to bypass their control and th eonly beings capable for destroying their story.
Retrace LXV. Everything you thought you knew is a lie, nearly every reference to Glen and Jack has to be reversed or re-examined, and Oz's "sin" suddenly makes a lot of sense.
Jack's friendship with Gil, Vince, and Alice is a reference to Lewis Carroll's child friends. In fact, Jack is very possibly based off Carroll. The anime even includes a scene in which Jack and the Will of the Abyss are taking a boat ride together, something Carroll was fond of doing with Alice Liddell and her sisters and which was what spawned the original Alice's Adventures in Wonderland.
Ada's fascination in the occult is also based on LC's own interest in the occult and ESP.
Oz's near-suicidal selflessness and his ability to use B-Rabbit's scythe make perfect sense as of Retrace LXX: Oz (Reality). He is the chain B-Rabbit, originally a rabbit doll brought to the Core of the Abyss by Lacie and imbued with life. Retrace LXXVI reveals how Alice came to become the B-rabbit. After killing her mortal body, she willingly fuses her spirit with B-rabbit's in order to protect Oz and keep him from having to kill anyone else.
As of Retrace LXX it's been revealed that Oz is actually the Bloodstained Black Rabbit and is in fact using Jack's body. Didn't we see Oscar being told that there's a possibility that baby Oz was switched with another child at birth?
And even further, it finally explains Oz's almost blind devotion to Alice, which seemed to just be an "it's love, don't argue with it" concept before this point. He was literally created with no other purpose in life than to protect Alice.
Consider how Alice, since the very early chapters, has been referring to Oz as her property. With the revelation that Oz used to be her stuffed rabbit in mind, her possessive claims actually make sense.
Jack's anger toward Isla Yura might seem a bit strange for someone normally so calm and friendly, especially since they share the same goal. But it makes perfect sense if you realize that Isla Yura was trying to toss the world into the Abyss just for fun, which Jack would naturally see as an insult to Lacie's wish, or at least his interpretation of it.
Oz's bizarre Freakout in Chapter 41, when he states that he has to destroy 'it', including a seemingly random panel of the Tragedy of Sablier makes sense when you realize that his shaken mental state almost broke the seal on his memories and made him recall Jack's command to destroy the Chains that support the world.
Gil's gotten lucky a lot. He's survived Oz slashing him across the chest, survived a direct hit from Cheshire, survived a poisoning attempt, and that's just the start. It's a sign of him being a Baskerville.
Oz's sin being his very existence: We now know that his body is actually Jack's body and that Jack murdered Zai's biological son in order take his place for his own designs. Oz is actually the consciousness of the true, original B-Rabbit, currently residing in Jack's cursed body. Poor Oz just can't catch a break...
From the very first chapter of the manga, we have the scene in which Oz touches the pocket watch for the first time and has an apparent hallucination of being hugged and then subsequently attacked by Alice. This scene doesn't make much sense until much later in the manga when Jack's intentions are finally revealed: What Oz experiences appears to be a corrupted, distorted memory from around the time of Retrace LXXVII where the Will is still very much infatuated with jack, to her own detriment, and Alice despises him for what he did to Oz. Believing him to be Jack, the Will hugs Oz and claims she's happy he came to see her before losing control of the twins' shared body to Alice, who attempts to kill him while telling him she'll never forgive him. Turns out that whole scene isn't there just to be creepy - it really is a brilliant bit of Foreshadowing.
Children of Misfortune are often born close to the one who will inherit Glen's soul, as with the case of Oswald and Lacie. Gilbert was supposed to be the next Glen 100 years prior but it was thwarted, which explains why Vincent has only one red eye.