Cancelled Champions

Averdian

Averdrian is an unreleased League of Legends champion that was rumored to be a predecessor to Heimerdinger. This rumor was later rebuked by the Associate Game Designer Coronach. It seems that this champion was a personal favorite of the Lead Effects Artist Nocturne, who used him as an avatar for quite some time and even stated on some occasions that he is working hard on implementing Averidrian to the game. Although his dream never came to fruition, Averdian did make his appearance on the Fields of Justice during the 2010 Harrowing event: lying dead in a coffin.




Gavid, The Plant King
The Plant King was scrapped due to not fitting within the League of Legends art style. It was rumored that he was later 
redesigned as 'Maokai', but looking at the names of his datamined skills and abilities, it is also likely that 'Zyra' was in some way based on this champion. If this is the case, she certainly looks more pleasing to the eyes… for a plant I mean! In the 2010 Harrowing event, Gavid also made his appearance on the Fields of Justice: dead in a coffin.



Tabu, The Voodoo Shaman

Tabu was probably based on Voljin, the Witch Doctor from the Warcraft III DotA mod, but it seems that for some reason he did not make the cut and was never introduced to the game as a playable champion. It is speculated that the Witch Doctor may have been reworked into a champion that we know today as 'Swain'. He did also make an appearance during the 2010 Harrowing event: dead in a coffin. 





Priscilla, the Spider Queen
This "lovely" lady was probably based on the famous DotA hero "Broodmother". This champion initially got shelved, but her concept was later used for "Elise, the Spider Queen" that was released for the Harrowing event in 2012. There were speculations that this champion was used as the basis for 'Urgot' due to similarities in some of the art assets, but this rumor was debunked later.



Well, the Hydrosoul
This unreleased champion, also referred to as 'The Water Wizard', is probably the only one that had a fleshed out backstory prior to his cancellation… at least to our knowledge. Some elements mentioned in his lore resemble the story of 'Damphair', a character from George Martin's "Song of Ice and Fire" book series. Prior to the recent release of 'Nami', Well was the only champion that used the elemental power of water to cast his wrath upon his enemies in the Fields of Justice. He also had a companion that he could summon in the form of a cute little Seahorse.

Omen

This demonic looking creature was actually very close to being released. He was shelved at the last moment due to mixed feelings in the Riot development team. This caused the delay of patch V1.0.0.125 since Riot had to push up the release of Riven to fill in the empty void left by the cancellation of this champion. It is rumored that Omen is just shelved for the moment until the development team makes additional changes on the champion to make him fully desirable by all Riot Staff members, as only 50% supported his release at the time.

Urf, The Manatee

Although Urf was just an April Fools' joke, he is one of the most memorable champions that was never actually introduced to the game as a playable character. He made his first appearance on April 1st, 2009 when Riot announced that he was entering the beta testing stage as an April Fools' joke. Alas, one year later, Urf met his demise by the hands of 'Warwick', who used his skin as a coat. This "Urf the Mantee Warwick" skin was made available for purchase to all players for a limited time. Thanks to the community response, all the proceeds went to the "SaveTheManatee.org", a charitable organization dedicated to the preservation of these majestic creatures. In addition, "Urf the Manatee Memorial Contest" was held by Riot games, who decided to give out some prizes for best community contributions to the "Urf Day" in the form of songs, artwork, videos and poems. A similar contest was held again in 2012.

Beside Warwick's special skin, Urf made his appearance in two different champion skins that are still available to players including Urf Raider Corki and the splash art for Fisherman Fizz.

Read about a special Warwick and Urf interaction here: http://lolextremegaming.blogspot.se/2013/06/haloween-map-easter-egg-2.html

Others

There are a few other cancelled champions that were hard to gather any specific information. This includes the 'Eagle Rider' that was probably based on the Warcraft III unit 'Gryphon Rider', 'The Iron Engineer' who looks like really close relative of 'Blitzcrank' and 'Tiki' that has a strong World of Warcraft vibe. 

SOURCE: http://www.in2lol.com/en/news/5615-fun-league-of-legends-facts-part-2