Roost can be obtained by breedin with these Pokemon:
- Pidgey, Pidgeot, Pidgeotto
- Spearow, Fearow
- Hoothoot, Noctowl
- Wingull, Pelliper
- Pidove, Tranquill, Unfezant
- Ducklett, Swanna
If Mandibuzz is female there is an 80% chance that the ability will be passed down.
>Starting in Black 2 and White 2, there is an 80% chance that the Ability slot of the female will be passed to the baby.
Just give the parent whose nature you want passed down an Everstone. It will work every time.
>From Black 2 and White 2 onward, if one parent holds an Everstone, its Nature will always be passed down. If both parents are holding an Everstone, a parent's Nature will still always be passed down, but which parent's Nature is passed down is randomly determined.
Hope I helped.