PuppyChung: His eyes have paw prints for pupils and his hair looks like puppy ears.
PikaChung: Both ends of his hair have a patch that resembles a certain Pokemon's ears. Once the Shelling Guardian/Tactical Trooper class line came out, this was applyed to them due to how those bits stick up like ears.
Chungdam: His futuristic armors and his cannon has led to him being mistaken for a Gundam. Especially as Tactical Trooper.
Chungina: A female variation of Chung, used due to frequently being mistaken for a girl, on account of his young, and overly cute looks. This nickname began to fade away as he takes on Shooting Guardian route, but is further enhanced as Fury Guardian. Greatly enhanced during the 2011 April Fool's Day event in Korean version, when all characters have been Gender Swapped.
Chung's Iron Paladin promotion (upgraded from Fury Guardian) further enforces it; his hair is down to his rear, and his armor gains three inch heels. Some of the promotional art for this form has a distinctly hourglass-ish waist, too.
Iron Princess: Chung's Iron Paladin class is called this, due to the above.
Elboy: The fandom's Affectionate Nickname for the titular character (and to disambiguate him from the title itself).
Elebro: Elesis during the April Fool 2014 event in KR
Add is what happens if Syura traded good old fisticuffs for technology.
Official Fan-Submitted Content: Most servers around the world usually hold annual contests for costume designing and, occasionally, accessory designing.
What Could Have Been: During development, the character Elsword was originally meant to be related with Elesis from Grand Chase, and Aisha and Rena were originally named Arme and Lire respectively. However, due the copyright reasons and Elsword and Grand Chase being hosted by different companies, this idea was scrapped.
However, due to Elesis' introduction in the Korean server, and her being the same person as Elsa, Elsword himself gains his official surname: Sieghart.
Initial plans for Sakra Devanam's designs were to emphasize her curves more and give her more provocative movements and poses, but this was decided against. Signs can be seen on the artist Sando's home page a few pages back Here (While safe for work, may have some mildly provocative pictures.)
Yama Raja which appears to be the 'sexier' class is done by another artist known as Slyph.
By digging in to the client data, you'll find that Raven's Sword Taker class was originally named Soul Taker. The fact that he can leech opponents' HP with one (later two) skill as well as the text "+300 SOUL" when you used an Awakening Potion may be a reference to this. Later on they did make a class with a similar, but more developed concept: Elesis' Dark Knight.