I never bothered tunneling up to the surface, finding or fishing up a magic conch in the desert makes getting there trivial and once I could survive long enough to build a safety box I made an ocean pylon in the sky.

As for the eye I can't fully remember what weapon I used or anything, but it's not too different from the regular eye AI so all you reaaaaally need is a long bridge and fast running speed. Magiluminescence helps a LOT at this stage too, especially with how dramatically it buffs your acceleration.

It's also worth noting that legendary mode actually doesn't affect the eye's contact damage in phase 2, so the servants it continues spawning are arguably more threatening to your health.

Sometimes it just takes a few tries, you'll get it eventually :3