This is pretty fun :) -- the controls are definitely more challenging than Agar.io, which uses the mouse for movement. I would caution the author to be ready for the possibility of a DMCA letter from Minclip [1], the company that now owns the rights to the game and is aggressively attacking all "clones" of the Agar.io game. Vanar.io seems different enough, but the letter has some strong wording such as "The URL is a deliberate attempt to create a false association with the Agario game, take advantage of the goodwill and reputation in the Agario game and divert users of the Agario game to the URL". Discussion and another example is on reddit [2]. So far the only Agar.io clones sent a letter are ones that directly copied and used the javascript code, so hopefully that's not the case here.
I played the game, got really good at it, and then quit because the company refuses to do anything about the teaming problems associated with FFA and the mind numbing issues with lag. It doesn't surprise me one bit that they are spending their time and efforts trying to attack others while Rome burns.
[1] https://github.com/github/dmca/blob/d028f601f93e201186b4a75b...
[2] https://www.reddit.com/r/Agario/comments/3f7oys/miniclip_sta...