The Flyff synth is a simple waveform with a little bit of a layered.. bell sample, maybe? Lots of portamento (glide), reverb, and vibrato.
The Maple Story synth is similar but with no bell layer.
The third synth is pretty different. Hard to say what but it's not a simple waveform.
I think you'll get closest by starting with a sine wave in something like an additive synth, and then add a little bit of extra harmonics there. The thing that really gives these songs a similar feel though is the combination of glide + reverb + vibrato.