Frankystein Mark II follows a distinct pattern: first, he generates a burst of steam, then on the next turn he attacks (either tearing into you or throwing a punch), then on the next turn he generates a burst of steam, and so on.

If you're in bad shape after fighting Franky, you should heal up during the first turn (since Frankystein isn't going to hit you on the first turn anyway), and then once you're healed up you should be able to fairly easily bash Frankystein into oblivion. Just keep your HP above about 15HP or so, at least on the turns before Frankystein's attacks.

Level 5 is about the lowest level that gives you a chance of defeating Frankystein Mark II.

Once you defeat Frank and Frankystein Mark II, you can continue on to Giant Step.