Cheesed The First Boss to Death

Got a full suit of Silver armor and the Iron bow, built a small structure of dirt with a hole at the top and just shot him for like 10 straight minutes. He basically can't hit you unless he fires a REALLY lucky spawn into the hole, which is why I would suggest getting silver armor because without it the army penguins will tear you to shreds.

At about 1/2 HP he starts randomly cloaking. He can still be hit while invisible though.

At about 1/3 remaining health he starts spawning mini UFO's that circle him and shoot at you. They only do 2 damage with silver armor on though, so basically they are mosquitos and you should ignore them.

When he dies, all the UFO's die but the penguin soldiers stick around, so make sure you deal with them.

His graphics change to show damage as he loses health, which is pretty cool.

When he dies, he drops the thing you need for the next version of the anvil that lets you craft steel and items using steel.

I'd suggest bringing some bandages to the fight, because even with silver armor the penguin soldiers and main UFO attacks do around 10 damage each.