Bahamut, the Leviathan
Lore
A mermaids tale goes like this:
The great king of the depths, nothing compares to his might.
When there's a threat to the seas, he will emerge into sight.
Explanation
A level 10 unit with incredible Attack and Defense.
With him on your field, you will not lose in a fight.
'Marine Snow Sacrifice' is recommended to help with summoning him.