Board Thread:Game Discussions/@comment-24998635-20140717163021/@comment-24829740-20140718131447

It is really based on your armor strength and elemental counters more than anything you can possibly influence. Yeah, you have to manage your friend hires and get powerful friends, but if you don't have a strong mono-earth or earth/wind armor you will struggle with this boss.

Keep in mind that Cosmos is 2% stronger than a regular EB, meaning by level 30 he is about 1 level ahead. Killing Cosmos at 43 will be like killing a regular EB at 45+.