first condition is to have done all the elin quest - gun, plasma. Second - need to build submarine and 6 black bombs.
For black bombs i need 6 sulfur and 6 phosphorisation. Sulfur - collect in 3 hours with 9 chars from kelan cave mine. And Phosphor is rare drop from mushrooms.
First Need to go to the doctor in olsya and ask him for the memory of elin. He will say to bring him come memory crystal. You need to go to the well in holy to the place where you take elin. There you will take crystal. Bring it back to the doctor.
Next you need to make the Black bombs.
Then go under sea. You must go on RIGHT side of the map and change map 4 times and in the end you will see doors of the ets horbour.
Go inside. You will see 6 another elins where you will place the bombs to destroy them.
Then ETs will come and fight. They are lvl 100s and with 10-11k HP. But they do much seal. But they are not very fast - prob like 600 spd they got.
After you defeat them you need to go to south pole. The empty house next to the hotel. There You click on the vase on table and door will open. Go inside.
Here you will meet Other ETS and dark elin wich will defeat you in any case - even her normal atk makes 1k dmg. But she dont spawn you. After she beat you will see the sad screen with half of the body of Elin. And she will die. Dont forget to remove her gears before death. And then another easy fight with same ETs from undersea.
After you beat them get 3 stars and capsule.
Next you need to go to holy to revive you pet. Talk with Abba and make wish for Elin. Need to pay 5 stas for revive. And she join your team. Other interesting part that after revive she is on same amity and same % of xp. My eli nwas lvl 155 77% and she keep them... till reborn XD.
Then need to go to hanging garden. Back jungle. Then inside the cave find the priest And just talk with him. No need to pay anything and he rb you pet. You have luck to choose what stats to have your elin and she add 129 skill points.
Mine become with 379 spd and 2k con and 700 sp. Wich is not bad for her level.
She learn the laser skill but NO TERRAFICATION as wlo homepage says... :P
And her new plasma got 75 atk.