Once a Cephalo has emerged it is suggested that you move away from it due to its long reach. Once at a safe distance aim at the actual parasite itself as the body takes very little damage, if the Cephalo gets too close try and use a shotgun to knock it back. However, if you have a flash grenade do not hesitate to use it as it will instantly kill it. Interestingly although a Cephalo can no longer be stalled, it can still be downed and you can use special melee attacks on them at that time, although this is no longer a one hit kill. With any fully upgraded magnum it takes only one hit anywhere on the Cephalo parasite or the host's body to eliminate attacks.
If you suspect a Majini might turn into a Cephalo it is then it is recommended that you shoot them in the kneecap. This should cause an attack prompt to show up. Go around the back and then use Sheva's throat slice, Chris's neck breaker, Excella's First Aid and Jill's Knee neckbreaker this should prevent the parasite from emerging.
The most often used attack is a slam in which it will slam you to the floor if at a close enough range.
A regular slash will also be used on occasion if you are too far for a slam attack.
Cephalo are also capable of slashing at you from the floor and when getting back up.