The unlock text for the 4th Hero reads "Reach 10 level with Endless runewords".

Now, I'm wondering. So far I've unlocked "Lucky", "Fresh Blood" and "Spell Breaker" runewords. Is "endless" just a generic name for The Runewords in general, and you just need one of them active for the unlock to happen? Haven't seen them refered to as "endless" anywhere else. Or alternatively, is "Endless" a specific runeword I haven't yet unlocked, and I should stop throwing my runes away on runs until I get it?

Or does it require ALL the runewords unlocked and active during a run?


Any ideas?

As i've found it here, you only get the "endless" runeword when you finish the game:
http://runestonekeeper.wikia.com/wiki/Heroes

So, its up to you how you beat the game.

The plural, "runewords", is pretty misleading here. It really doesn't make it sound like it's talking about a particular runeword called "Endless". The developer should probably patch that typo out.