pity

An expert staff ghost is like any other ghost, the only diference is that they're extremely fast. You can unlock them once you have beaten a certain record on a course. For example, your first ghost race is against any worldwide ghost (choosen randomly) if you beat that ghost you will race against a fast staff ghost and if you beat that ghost you'll race an expert staff ghost. These are made by the ones who created the game, so they're more likely to use shortcuts on the course so be prepared. Oh and a retro course is the one that came from a past game, like N64 mario raceway or DS yoshi falls. And the retro cups are the shell, banana, leaf and lightning cups, as they contain only retro courses. Hope this helps!

pity

Here are the times for every staff ghost and the times to unlock expert staff ghosts:

Mushroom Cup:

Luigi Circuit
Normal Staff Ghost Time: 01:29.670
Unlock Time: 01:25.742

Moo Moo Meadows
Normal Staff Ghost Time: 01:37.856
Unlock Time: 01.33.571

Mushroom Gorge
Normal Staff Ghost Time: 02:16.110
Unlock Time: 02.07.755

Toad's Factory
Normal Staff Ghost Time: 02:22.480
Unlock Time: 02.15.681

Flower Cup:

Mario Circuit
Normal Staff Ghost Time: 01:44.777
Unlock Time: 01.39.183

Coconut Mall
Normal Staff Ghost Time: 02:30.764
Unlock Time: 02.24.788

DK's Snowboard Cross
Normal Staff Ghost Time: 02:34.693
Unlock Time: 02.24.725

Wario's Gold Mine
Normal Staff Ghost Time: 02:19.583
Unlock Time: 02.14.932

Star Cup:

Daisy Circuit
Normal Staff Ghost Time: 0:56.822
Unlock Time: 01.48.791

Koopa Cape
Normal Staff Ghost Time: 03:03.022
Unlock Time: 02.54.897

Maple Treeway
Normal Staff Ghost Time: 02:58.633
Unlock Time: 02.50.229

Grumble Volcano
Normal Staff Ghost Time: 02:28.237
Unlock Time: 02.19.524

Special Cup:

Dry Dry Ruins
Normal Staff Ghost Time: 02:30.949
Unlock Time: 02.21.681

Moonview Highway
Normal Staff Ghost Time: 02:16.802
Unlock Time: 02.07.016

Bowser's Castle
Normal Staff Ghost Time: 03:04.836
Unlock Time: 02.55.017

Rainbow Road
Normal Staff Ghost Time: 03:05.895
Unlock Time: 02.59.293

Shell Cup:

GCN Peach Beach
Normal Staff Ghost Time: 01:34.233
Unlock Time: 01.30.698

DS Yoshi Falls
Normal Staff Ghost Time: 01:16.461
Unlock Time: 01.12.901

SNES Ghost Valley 2
Normal Staff Ghost Time: 01:06.595
Unlock Time: 01.03.752

N64 Mario Raceway
Normal Staff Ghost Time: 02:14.799
Unlock Time: 02.07.915

Banana Cup:

N64 Sherbet Land
Normal Staff Ghost Time: 02:48.651
Unlock Time: 02.37.784

GBA Shy Guy Beach
Normal Staff Ghost Time: 01:45.568
Unlock Time: 01.39.255

DS Delfino Square
Normal Staff Ghost Time: 02:41.807
Unlock Time: 02.33.107

GCN Waluigi Stadium
Normal Staff Ghost Time: 02:32.882
Unlock Time: 02.24.645

Leaf Cup:

DS Desert Hills
Normal Staff Ghost Time: 02:10.233
Unlock Time: 02.01.141

GBA Bowser Castle 3
Normal Staff Ghost Time: 02:58.304
Unlock Time: 02.50.637

N64 DK's Jungle Parkway
Normal Staff Ghost Time: 02:58.264
Unlock Time: 02.49.028

GCN Mario Circuit
Normal Staff Ghost Time: 01:59.771
Unlock Time: 01.55.267

Lightning Cup:

SNES Mario Circuit 3
Normal Staff Ghost Time: 01:38.880
Unlock Time: 01.34.828

DS Peach Gardens
Normal Staff Ghost Time: 02:34.894
Unlock Time: 02.29.006

GCN DK Mountain
Normal Staff Ghost Time: 02:57.744
Unlock Time: 02.50.248

N64 Bowser's Castle
Normal Staff Ghost Time: 03:19.323
Unlock Time: 03.06.723

Hope this helps!!!