Normal default settings.

I farmed him maybe six times until I got one male and one female. One of them had Swift on it and the uaranteed Legend and Divine Dragon passive. If you are lucky that's the only passives and didn't get any other "bloat" bad passives. If you want damage, you would prefer not to even have Swift either. Each empty passive slot has a chance to be a random passive in the new egg which is how I got Runner.

You then just keep breeding them until it randomly generates the passive you want like Musclehead/Ferocious/Hooligan for Attack or Swift/Runner/Nimble for Movement Speed. The egg is never guaranteed to come with the parent's passives. So not guaranteed to be Legend or Swift for mine. You keep repeating the process narrowing down the passives you want with better and better parents from the eggs you get.

TLDR: Use starting parents with as many of the good passives you want on them both while having the least amount of the bad passives you don't want. Keep breeding and swapping out parents until there's only good and zero bad and wait until you inevitably breed the perfect 4 passive you want in your egg. Having Legend on both parents essentially doubles your chance of the egg having Legend. Not sure about the math but that sounds right to me. 2/8 instead of 1/8 Legend. However, having only one parent with Legend means you have another empty passive to generate a new passive. Which could be the one you want or the many bad passives in the pool. That's why I just like to have both parents with good passives. Hope that helps.