The damages are percentages of his current max HP. I think his basic is 20%, AoE is 16%, and crawl is 30%. From there it is pretty easy to calculate the base damage you can expect from his attacks (current HP x ability %).
GG damages his droids and gains a bonus to his HP at the start of all his turns, including his bonus turns.
G13 is huge for GG. He'll easily have over 100k base HP at G13. Then he'll gain 20% at the start of his first turn assuming all allies are still alive and are droids for a massive 120k+ starting HP, giving his AoE a base damage of 20k non-crit, and it goes up from there very quickly with bonus turns.
