uh-uh there is another ending if you have 100%...and that ending you are talking about,slythe,is the one that after yuna fights with ixion,ixion jumps at yuna and she falls through the hole...and then,at the en of the chapter,when yuna is all alone in the darkness,you have to press R1 all the time to hear some times some whistlings,and tidus shade will appear some times,and at the end(after fighting the boss) the faith boy asks you if you want to see "him" again,and if you answer yes,after the credits,it opens with the ffX ending(tidus is in the sea) and wel,then they meet at besaid.the one that you get after getting the 100% is the cutscene where yuna and tidus are talking in zanarkand,and she says,"are you a dream this time" and he says " i dunno" and then she pushes him,he falls,they laugh and yuna says " dunno what to say...this all started,when i saw the sphere of you" and there it ends...
DDD i played it 27 times O_________O XDDDDDDDDD