Well, the problem with disappearing upon turning left should be fixed in the newest release from earlier today. If you redownload C2, you should find that that doesn't happen anymore.
Actually, the 1-pixel-floating thing might be fixed too when you update depending on how old your version is. Either way, I'll take a look and see if I can come up with anything else.
EDIT: Well, I helped remove a bit of the "jankiness" as you call it. <img src="smileys/smiley17.gif" border="0" align="middle" />
db.tt/oPFExVJq
He no longer jitters around while running, and the animation works properly now too. For the jittering, you have to make sure that the origin point of each frame in the animation is set to the same height. You can see it by going to "Edit animations", then click on the "Set origin and image points" button towards the top left. If they aren't lined up right, you'll get that sort of result.
And for the animation playing properly, remember to set it to looping by clicking the animation name and setting Loop to Yes over on the left. <img src="smileys/smiley2.gif" border="0" align="middle" />