The first one is correct. "Faster" is the correct word

"more fast" is incorrect. It is a short word so the comparative is faster, not more fast. The conditional part is correct.

From the sentence you are using it would be: 1. If I were lighter, I could fly faster.

"If I were lighter, I could fly faster" is the correct answer. When creating the comparative form of an adjective, all short, 1-2 syllable adjectives simply add an "er" to the end: longer, faster, greater, poorer, tighter, etc. Some of those types of adjectives have doubled consonants: bigger, taller, hotter, etc. For longer adjectives with 3 syllables or more, you use "more + (adjective)" more interesting, more difficult, more peaceful, etc. There are exceptions though, so you just have to remember them: more fun, good > better, far > farther, etc. This is just a quick description of some of the rules for adjectives in the comparative form. There are more details to be known, so have a look at this link if you would like to learn it: http://www.eflnet.com/tutorials/adjcompsup.php I hope this helps! Good luck in your studies!