Board Thread:Manga/@comment-28516743-20170603033410/@comment-31641135-20170603091831

Well one possibility could be a weapon capable of cutting through Reiner's titan armour as that there main concern due to them needing to come close to even hurt him as they have no ranged weapons which can damage Reiner so Eren could potentially make a sword or something out of the crystal stuff which could cut through the armour.

Alternatively, maybe he could use if for creating blockades and cover for the squad so they can rest up or plant traps. A far stretched use of the power would be somewhat armouring up Armin so practically untouchable as hes already slow so it wouldn't really hinder him.

It could also be used to upgrade the squad's weapons and maybe even provide them with a form of light armour to wear so they dont go splat so easily.