I have no problem with you making a Wonderland fangame, as long as a few rules are followed:
a) no 'official' (and hence copyrighted) material is used (official graphics, sound fx, music, copies of gameplay mechanics)
b) the game is not distributed other than on this forum or on a wonderland fan site (e.g. mette's site)
c) the title screen includes the remark that the game is not "official" and hence Midnight Syngery has no responsibility for its content.
d) the spirit of the game doesn't deviate too far from the official Wonderland games (e.g. a violent shoot-em-up where Stinky and Loof battle hordes of Zombies would not be ok)
Hopefully you'll find that these are reasonable (and not too restrictive) requests.
Cheers,
Patrick