I would move Petterd (20yo, 20 games), Buckley (22yo, 21games) and Meesen (22yo, 6 games) into players Melbourne is relying on becoming category A or B.
Pettard has shown promise up forward with limited supply, has shown in other games he can play defence or midfield as well.
Buckley has had a horror year of injuries, showed good potential in his previous two years. Possible missing link in midfield to break through packs?
Meesen was really good in the ruck before getting injured.