The highest monster in RuneScape is the Corporeal Beast, at level 785 with 20,000 Life points it can be very difficult to slay.
It is recommended to have high combat stats, 90+ before trying to take on the Corporeal Beast. You should also consider taking a team. You can find a team in the Monster section of the Runescape Forums.
The monster has a maximum melee hit of 513 and a maximum magic hit of 650. It has very high defense and life point levels, making it extremely hard to solo.
Gravestones cannot be obtained in the area. However, players have 2 minutes to return to the cave and pick up their items if they happen to die. To get back in time, it's useful to have a death spawn at Soul Wars. Grab a Super energy out of the bank, teleport to Clan Wars and run back. A grave will appear as usual, however, for players who die outside of the area.