Now this may be glitched. I'm not sure. But everything you can destroy with a thrown shield seems to count.
Pressing L1 until your shield is up and then pressibg R2 will throw the shield in any direction your reticle is aiming at.
Obviously enemies count and that is a good way to rack up takedown kills also, plus it can even ocassionally help with the deathblow count (when an enemy gets an orangey kind of mark over their body).
The other thing that counts is seals. Some chests have three seals to break before you unlock them, all three count towards the trophy. The seal at the "prisoner" towards the end of the first water rhealm mission also counts.