Expert staff ghosts are time trial records added by the game devolopers .The unlock them you need to beat the normal staff ghost's time by 3-10 seconds at least.Expert staff ghosts are an extra challenge.They can unlock characters or even bikes and karts.I will tell you some of the characters that you need to unlock expert staff ghosts.Wegee circuit's expert staff ghost time is 1 minute 19 seconds(Excluding the .0987 number).So you could beat a staff ghost by like 10 seconds or so and you could beat or end up close to an expert staff ghost's time.
|Baby Luigi||Unlock 8 expert staff ghosts|
|Funky Kong||Unlock 4 expert staff ghosts|
|Torpedo||Unlock 12 expert staff ghosts|
|B-dasher NK2||Unlock 24 expert staff ghosts|
|Mii(Outfit B)||Unlock all 32 expert staff ghosts|