Your shiny Celebi would cost 10,000 to transfer, because it's a shiny Mythical. Standard shiny Legendaries cost 10,000 as well. Here's a cost chart I found on this website: Also....
If a Pokemon would cost more than the maximum of 10,000 energy to transfer - for instance, a shiny CP 2400 Mythical Pokemon - it counts as using all of your energy but still may be transferred.
Standard Pokemon
Criteria ---> Cost
Normal Pokemon ---> 10
Shiny ---> +1990
CP 1001-2000 ---> +100
CP 2001+ ---> +300
Legendary Pokemon
Normal Pokemon ---> 1000
Shiny ---> +9000
CP 1001-2000 ---> +300
CP 2001+ ---> +500
Mythical Pokemon
Normal Pokemon ---> 2000
Shiny ---> +8000
CP 1001-2000 ---> +500
CP 2001+ ---> +700
