Lissandra does not use her name within the League in-story. To keep her cover as Lissandra in Freljord she is only listed as "The Ice Witch" in the League .
The Ice Witch's original name is Lissandra. When taking over Queen Mauvole she named her successor Lissandra so when the Ice Witch took her identity she reclaimed her own name .
Lissandra's lore resembles Ultimecia's story from Final Fantasy VIII where she possesses different sorceresses from different time periods, deceiving people to achieve her goal of ruling the world in all time periods. Her Ice Shard skill resembles sorceress Edea's Ice Strike.
Lissandra's character shares a lot of similarities with Akasha from Unreal Tournament III, including their eternal life, accent, quotes, and ambitions to destroy the world.
Lissandra also slightly resembles Flemeth from Dragon Age, while Flemeth possesses and takes over her "daughter" Lissandra steals her successors' identity much like Flemeth with her daughters.
The event between Ashe, Sejuani, and Lissandra is similar to "The Hunt is On!" called "Battle for Freljord". This makes it the second event to happen in-game but is not directly tied to the lore. However unlike "The Hunt is On" , the "Battle for Freljord" has no actual gameplay impact.
Lissandra remains the only champion to possess a unit-targeted ability (Frozen Tomb) that can be self-cast but not ally-cast.
Lissandra is the second champion to feature a monologue on her login screen, being preceded by Elise and succeeded by Lucian.
In one of her monologues she mentions she lived before the fall of the Shuriman civilacions ("before the Desert shallowed Shurima'"). Considering that Xerath's ascension also predates such events, they might have lived their original human lives at the same time.
Lissandra possesses the only in-game monologue in League of Legends - 30 seconds after a victory in the Howling Abyss, she will begin a lengthy dialogue speaking about the Watchers, Serylda and Avarosa.
Lissandra's is blind in the sense that her eyes do not work, mauled by an ursine prior to becoming Iceborn . However, she is capable of sensing her surroundings through ice
Lissandra's is the only champion to perform high screams and shouts when using any of her basic abilities (even for her ultimate that is more calmed, she still harshly "yells"). Combined with that fact that she is much more sensible to sounds due to her blindness, she may also use echo location to guide herself
Centuries ago, there were three sisters: Avarosa, Serylda and Lissandra. They lived under reign of The Watchers who granted them power and immortality, dubbing them Iceborn. Avarosa started a rebellion against The Watchers, and Freljord was divided. Lissandra supplanted her own successors to hide her immortality, naming her final heir Lissandra so that she may claim her own name back. Ashe descends from Avarosa and Sejuani from Serylda, making Lissandra their ancient ancestor .
Anivia and Volibear were aware of the presence of a great evil in Freljord. This great evil is most likely The Ice Witch.
Anivia was made aware of it by her ties with Freljord's magic. She felt it slowly being corrupted and turning it into black ice. The Ice Witch's magic is black ice.
Volibear was made aware of it by the maelstrom's vision. He saw creatures of ice slaughter the remaining Ursines. These creatures are most likely the Watchers.
Trundle made a deal with The Ice Witch after he tried to steal her enchanted ice club, Boneshiver. In exchange for it, he promised her a troll army, once he overthrew the chieftains of each troll tribe with the help of the club.
According to Greyor, Lissandra was the leader of the Iceborn before the rebellion, making the Seeker's Armguard hers.
"We have waited so long for this day, we have been so patient. Now, my children, my Frostguard, it is our time.
"I have seen the future, and it is cold. The Watchers return and they are so pleased with you. They will take away your hunger. They will take away your pain. You will be reborn; like me, you will become Iceborn."
"We will take back what is ours. The other tribes won't be able to stop us, they are but snowflakes. And we are an avalanche."