When you first reach Route 5 (Unova) Bianca will introduce you to Hidden Grottos. Inside you'll find a Minccino with the Skill Link ability.

After you have captured the Minccino from inside the Hidden Grotto, upon returning there you may find a Liepard with the Prankster ability.

There's a Crustle blocking the eastern exit of Seaside Cave. Using the Colress MCHN on it will wake it up.

Just as in Black and White, there's a load of pesky Foongus on Route 6 (Unova) and Route 7 (Unova) pretending to be Pokéballs..

Undella Bay is home to a Jellicent, but there are some differences as to what you'll find between the two games. In Black 2 a Male Jellicent will appear there on Mondays, but in White 2 a Female Jellicent will appear there on Thursdays. Both have the Damp ability.

Once you have seen all Pokémon in the Unova Dex, Professor Juniper will present you with a License, allowing you to travel to the Nature Preserve. Hidden in a clearing there you will find a Shiny Haxorus.

On Thursdays a Braviary with the Defiant ability will appear on Route 4 (Unova).

On Thursdays a Mandibuzz with the Weak Armor ability will appear on Route 4 (Unova).

Although the Relic Castle seems to have completely caved in, it is still possible to access it via a cave at the Pokemon World Tournament. Inside you will once again find a Volcarona. It is very low levelled, but if you defeat it it will reappear at a much stronger level in the same place after you have beaten the Elite Four.