Here is the rule for the monster I'm using next session; CR 7 Huge Ice Elemental
A creature with vulnerabilities takes half again as much damage (+50%) from a specific energy type, regardless of whether a saving throw is allowed or if the save is a success or failure. Creatures with a vulnerability that is not an energy type instead take a –4 penalty on saves against spells and effects that cause or use the listed vulnerability (such as spells with the light descriptor). Some creatures might suffer additional effects, as noted in their descriptions.
The party's 7th level Sorcerer will be using Faming Sphere (he loves this spell);
A burning globe of fire rolls in whichever direction you point and burns those it strikes. It moves 30 feet per round. As part of this movement, it can ascend or jump up to 30 feet to strike a target. If it enters a space with a creature, it stops moving for the round and deals 3d6 points of fire damage to that creature, though a successful Reflex save negates that damage. A flaming sphere rolls over barriers less than 4 feet tall. It ignites flammable substances it touches and illuminates the same area as a torch would.
The sphere moves as long as you actively direct it (a move action for you); otherwise, it merely stays at rest and burns. It can be extinguished by any means that would put out a normal fire of its size. The surface of the sphere has a spongy, yielding consistency and so does not cause damage except by its flame. It cannot push aside unwilling creatures or batter down large obstacles. A flaming sphere winks out if it exceeds the spell's range.
THREE QUESTIONS:
1) So the elemental may fail the required reflex of 16 a couple times and for example let's save the sorcerer rolls 10 points of damage and the elemental MAKES his save..this means 5 points of damage due to vulnerability ("regardless of whether a saving throw is allowed or if the save is a success or failure")?
2) Same situation but the elemental now FAILS his save and takes 10 points of damage from the sphere and 5 points of vulnerability for a total of 15 points?
3) Does the elemental add -4 to all his saves due to this effect being a spell? " instead take a –4 penalty on saves against spells and effects that cause or use the listed vulnerability (such as spells..."
1. No, the Elemental won't take any damage if the save is successful. But for spells with half damage on a reflex save it would still take 1.5 times the half damage (75%).
2. Yes, if it fails the save, it takes 150% of the damage rolled, 15 points in your example.
3. No. The description says "Creatures with a vulnerability that is not an energy type instead take a –4 penalty on saves against spells and effects that cause or use the listed vulnerability". That's for creature's that are vulnerable to poison or similar effects. Since the Elemental has just a vulnerability to an energy type, it doesn't suffer the -4 save penalty.