Some of the abilities the 4th/5th gen pokemon have are already in 3rd gen. If a 4th/5th gen pokemon has 2 brand new abilities that wasn't in the 3rd, I try to give them similar abilities. For example, I just inserted audino but none of it's abilities was in 3rd gen. So I simply gave it Chansey's abilities because they're both very similar. But Most of the 4th/5th gen pokemon at least have 1 ability that's already been in the 3rd. Some are the pokemon's DW Ability. Example, Durant's Swarm and Hustle.
As for the moves, it's the same thing. I just find animations that suit that particular attack I want to insert. Example, Featherdance looks ALOT like Roost. You can also go over very weak moves that barely any pokemon has such as Water Sport(That move that weakens fire type attacks...So useless because only water pokemon can learn that move but fire doesn't even hurt them! smh) I went over it for Scald.