The Manticore is a very powerful boss that only appears on epic and legendary. You encounter it in the Sandswept Cave on the east of the Fayum Desert. This monster has a plenty of ways to kill you, and extreme caution is required to survive this fight.
The Manticore has plenty of powerful attacks. The first is his lightning breath. This attack deals tons of lightning damage and is likely to one-shot unprepared characters. His second one is a "pounce" that does an incredible amount of damage. The Manticore performs this attack very quickly and you do not have much time to react. Another attack are projectiles that possibly deal bleeding damage. At any rate, avoid them. He can also make spikes appear out of the ground that deal poison damage. However, these are easy to avoid.
Even with lightning resistance at 60-80%, the lightning breath will still deal a lot of damage to you. Just try to avoid it, and run away if it hits you. The pounce is almost guaranteed to kill you in one hit. You could max out bleeding resistance if you want, but it will not make too much difference. When you see the Manticore rearing back, run in exactly the opposite direction from its mouth, as the pounce actually has an area of effect! The darts deal bleeding damage, so 50% bleeding resistance will help. The spikes deal poison damage, but they are easy to avoid.