Mokona is a little something Yuuko gave the gang before their journey begins.
Mokona has 108 different skills which include: he teleports the gang throughout the dimensions, he can sense Sakura's feathers (his eyes will bulge "Mekyo" when ever they are near), creating a window in order to speak with the Dimension Witch Yuuko, and he acts as a translator for them. When Mokona was kidnapped, the gang was at a loss because they could not understand each other's language.
More of Mokona's skills are listed
here
Digg
Furl
Del.icio.us
Google