Was playing DoE the other night after a long day with an early start 16hr day - the eyes were going fuzzy and my head was telling me to go to bed. Had just got some new troops so just wanted to fit them out before retiring.
Then whist going thru the army in groups of 4 (each row was the same type) I must have gone cross eyed and "boom" the whole lot turned 3D - each icon must be spaced perfectly so as to overlap each other, the numbers (ATK,DEF,HP) are pretty cool because they become a combination of the overlapping icons.
If you are a bit tired its easy - if you a awake just try the cross eyed thing once its focused you can scroll up and down (providing your troops are in groups of 4) they will all look 3D (note if you hit a line with different troops it messes with your head.)
It a trivial thing but I thought it was pretty cool when it happened - it just shows with a little bit of image offset and a pair of 3D glasses you could make the whole game 3D