Annie is currently the only champion to have 12 skins including Classic.
Annie is the second champion to have her ability icons remade with a Visual Update (the first being Katarina)
Summon Tibbers currently has the highest AP ratio in the game (515% with initial cast as well as all 45 ticks from Tibbers' aura)
Annie is the first fire-themed champion (the second being Brand)
Annie & Tibbers' names respectively come from a Riot Games Inc. Gameplay Producer's girlfriend and her favorite teddy bear.
Annie and her title of 'the Dark Child' draw inspiration from several sources:
Annie derives from Hebrew חַנָּה Ħannāh, from Semitic noun Ħann-at "grace", shared with Shauna Vayne & possibly Shyvana.
The conflict between Annie & her step-mother Leanna parodies the Wicked Stepmother trope, though observers could empathize with Leanna's rancor at Annie, whom Leanna blamed for the deaths of Leanna's daughter Daisy & Annie's father Gregori.
At one point she was to be bundled to celebrate her visual update (coupled with the fact the Collector's Edition was outdated) yet it never happened and as a result she became the first skin sale to ever be denied to the public.
Her Chinese artwork might have influenced her visual update.
Her International Updated splash art was further updated to the Chinese version. Previously she had a much more grim expression [S|L] where currently she has a more cheerful one. The Chinese edited version is a direct reference to the old Chinese splash art.
She references Alice in Wonderland (Annie is dressed as the titular Alice and Tibbers as the White Rabbit)
This skin was a response to the player request to have Tibbers with a different appearance. It was classified as Legendary back when it was released, but features present in today's Legendary skins (modified ability particles, different emote or recall animation, new voiceover, etc.) are absent from this one.
In Annie's current lore, Gregori's epithet is shortened to "the Gray" and Amoline is now just called "a witch".
Tibbers was hand-crafted by Annie's mother, with the mythical Shadow Bears as a template, and is the only memento she has of her. She uses it as a focus for her pyromancy to bring Tibbers to life as opposed to the previous lore when he was just a Shadow Bear whom Annie herself enthralled.
Annie's stepmother is named Leeana and her stepsister is named Daisy just like the SentinelIvern summons. It is unknown if these two are related or not.