Mustaine isn't rhythm guitar. He's co-lead, always has been. He does about half the solos of all Megadeth songs. Bass is actually a very complex instrument. I myself am a guitarist and drummer, but it's harder to become a good bassist than it is to become a good guitarist.
Well, first go here: http://animator.userbars.com/
Then click "Browse the Archive" the archive shows in new window, but don't close the old one, then search the archive and select bars you like, you can choose 10 bars.
Then, go to the old window and scroll down, you should see orange box with links of your chosen userbars, then change the Transition Effect to "fade" (my recommendation)
Then click "create" and you will have link of your userbar.