In the first stage, I pumped up the shooting speed and bullet speed, and also pumped up the damage & accuracy a little. Then, on the first ability, I chose vampirism, and started pumping only it. After a few improvements, vampirism will heal you a lot (!) of health almost every shot. After that, when the pumping of vampirism reaches its limit, it will be much easier, and even a bunch of turtles that come close to you will not be able to kill you, since you are constantly being treated. And then everything will go much easier, and it will be fun to pump in the rest of the abilities.
Yeah, I'm having like a god like run right now (actually since yesterday, have it open in the background).
am currently at level 154 or something, but basically I cant die anymore since those turtles jsut die before they can even touch .
Only reason why I am not further is cause I have to switch back to the game every now and then and click an upgrade.
and my notebooks fans running pretty wild, so dont wanna risk it shutting down due to heat.
but basically could get any score I want with enough time.
if you reach level 60, you have basically made it :-)
Edit: I'm currently level 338 and still counting :-)
Still seem to have 1 ability left to get though, luck wasnt on my side yet to have it offered