Castle on the Coast (UP)

Those are the big armored soldiers that you will come accross a couple of times during your adventure. The easiest and fastest way to grind this is by using the Forest Teleporter, exiting the room and turning right to reach the outdoor area. There will be 2 Armored guys. Beat them, go back to the Teleporter Room and kill yourself by jumping into the void. You will be teleported back to the last checkpoint, which is the room just before the Armored guys (which will have spawned back)

P.S. If you just simply jump in the water without going back the to Teleport Room, the Armored guys will not respawn !