How to run a bone devil(osyluth) encounter in Pathfinder

Bone Devilsare Lawful evil outsiders and as no surprise they are true devils. Being a true devil grants the bone devil several different abilities such as immunity to fire and the ability to see in even magical darkness. One of the more potent abilities being a true devil grants the Osyluth is the chance 1/day to summon another of its kind.

1/day—summon (level 4, 1 bone devil, 35%)

Bone devils also have an ability that causes anyone within five feet to flee in fear of this gruesome devil. Fortunately for enemies of the Bone devil this effect can only happen 1/day to any individual opponent. Unfortunately it is an automatic action to force an opponent to make the save.

fear aura (5 ft., DC 19, 1d6 rounds)

The bone devil has three abilities that allow for it to stalk its prey undetected. The first is the fact that as a standard action an unlimited number of times per day the Bone devil can become invisible. Even though this magic breaks when the creature attacks it is still very potent. Using invisibility along with fly and teleport the bone devil can stalk a party preparing for the perfect ambush. Not to mention that these abilities allow it to escape a battle that it appears to be losing.

Constant—fly,At will—invisibility(self only), greater teleport (self plus 50 lbs. of objects only),

The bone devils has within its grasp two major battle field control spells. While this may not seem especially powerful remember that these spells can be cast an unlimited number of times per day and do not break invisibility. Wall of ice can either make a 15' radius hemisphere or 120 square feet of ice as a plane. In eiter case the wall is a foot thick and has 36 hp.

At will—major image (DC 17), wall of ice

While not as being of game changer as some of its other abilities the poison from the Bone Devils scorpion like tail can leave its foes sapped of strength and unable to fight back. Combine the fact that the bone devil has a 10' reach and combat reflexes allowing it to make up to 6 Attacks of Opportunity a round; then a party can quickly feel the sting of the bone devil.

Poison (Ex) Sting—injury; save Fort DC 20; frequency 1/round for 6 rounds; effect 1d3 Str damage; cure 2 consecutive saves. The save DC is Constitution-based.

I always try to save the best for last. Even though it can only do this three times a day the ability to instantly become invisible as a swift action is incredibly powerful. a potent strategy with this is to make a full attack become invisible and take a 5 foot step leaving its opponents guessing where it was at.

3/day—quickened invisibility (self only)

Being that bonedevils can cast invisibility at will and unless they attack or take another hostile action they remain invisible for 2 hours one can assume that unless it is in combat the bone devil is probally invisible. Given that fact we can assume that it probally sees the party before they see it. If the party looks threatning and what adventuring party doesn't. The bone devil should teleport away to safety and try and summon a friend to help him. Eitehr way one or more invisible devils return shortly to begin harassing the party.

To trully scare the party have the bone devil approach while invisible. Undetected have the creature cast wall of ice forming a hemisphere 15' in diameter trapping it and a single party member away from the rest of the party. Due to the fact that Ice wall does not void invisiblity the Bonedivil is still invisible and the party has no idea what cast the walll of ice.

To continue to confuse the party in the first round of actual combat don't attack. Instead major image and have some other illusionary threat attack the party. Individuals who engage this apparition recieve a will save DC 17 to disbelieve the creature attacking them. Meanwhile Bone devil is breathing down the neck of the trapped party member.

In the second round the Bone devil should full attack the trapped individual. At this time unfortunate party member will need to make a will save or begin to cower if the ice wall has not been broken. If other party members try to come to aid thier teammate the bone devil uses its quickened invisiblity to hopefully void the attacks.

In the following rounds until the party has become a credible threat the bone devil continues making full attacks on the trapped individual. If the party does force the bonedevil to become invisible on its fowlowing turn it teleports outside of the sphere of ice.

With the party flodding into the hemisphere the bone devil conjures another illusion this tiem of its self hoping to draw the party out and begin icilating them again. On subsequent turns the creature starts making more domes of ice attempting to seggregate the party. Once it has sucsessfully isolated another weak target the Bone devil unleashes with a full attack. Again the creature must make a will save or cower in fear of the creature.

Using this strategy for the bone devil will cause your party to curse your name but will ultimately give them great satisfaction in overcoming this deadly creature