Iron God

[4D]

I assume the requirements are to kill every titan, in the same run?

[Oliarco]

Yep, the requierement is exaclty that. You also need to select the Iron Mode after finished the game but i guess you already know this.

As far as i understand you can unlock the achievement even in NO-New Game+ mode and you probably don't need to kill the secret bosses in order to unlock it.The "Elder" in the east secret area and the Black Plant after solved the puzzle in the forest

I tried in the past but some bosses are very hard to kill in 1 life like the Yeti or the Meteor, Heck the final boss is actually easier to kill in 1-life than many others in my opinion. It's even true that i start the game from time to time just for kill 1 or 2 times the White Baby so maybe is this the reason why i find it easier :)