The quality of your contribution is lacking. By itself, it'd be okay
for an amateur work. But superimposing it on a high-quality sprite
that's obviously from another source (Game Freaks' sprite) makes it a
lot worse. You'd do better to redraw the Mantine yourself: even if the
Mantine itself would not be as good, the combination of your sprite and
your sprite would be better than this.
I'm not that good of a sprite artist myself, but I at least know better
than to mix styles like that.
You might want to try sticking to small sprites for starters, so you can
gain an appreciation of the role of each individual pixel. It's hard to
consider the pixels individually when you're working on something as
large as what you have, but much easier when you're working on, say, a
32x32 or even 16x16 pixel image.