doing hard mode you get a good idea of what extreme mode will be like. its actually rather easy and I find titan and ifrit extreme to be harder than this
basically, you know where he is going to do his charge attack by the splash in the water. wherever it is, you don't want to be in a line in front of it because it covers the whole arena in a line...like titan landslide..
his body slam uses the same mechanic, just watch the splash and be on the opposite side of the arena from where it is. he only hits 2 sides of the arena. if you look at the ground you can see which sides get hit all the time, its always the same two. you need to be really far away or the body slam will suck you off the side.
kill adds as they spawn and kill the yellow orbs.
the hardest part is really just avoiding being knocked off but its really easy to avoid. just watch for the splash.