Tip: When you're going to run into one of the bigger zombies, pull a wheelie. This will allow you to knock them down and then tilt forwards, driving straight over them, with much less resistance than if you try to plow through them.
The easy achievement only totals how many you've killed in the final bubble I think. To make it easier, just make a custom arena with 25 of the weakest enemies, and only a single bubble. Should get it instantly.
Well, those "medium" badges should be easy. Took almost no effort to get them. An enjoyable game, but gets boring when you're scoring 500m+ on your second go. 4/5
Nice game, just wish you could zoom out more to see the whole level. To kill the boss: When he charges you, slash through him then. This will cause him to jump into the air, at which point you slash him there.