These latest online Missions allow you to recruit Riolu and Burmy (Trash Cloak), whether you own either Pokemon Mystery Dungeon: Explorers of Time or Pokemon Mystery Dungeon: Explorers of Darkness! As a bonus, each recruited Pokemon will hand you a valuable item!

Riolu Online Mission
Riolu had its Power Band stolen! Track down the sneaky Toxicroak responsible . It's hiding in Mt. Travail.

Burmey (Plant Cloat) Online Mission
Head over to Quicksand Cave and hunt down the Bastiodon that stole Brumy's Silver Gummi.

Source: http://www.pokemon.com/#dungeon2_24