Flat will save immunity?

[With a box]

Undead and construct has
Immunity to any effect that requires a Fortitude save
, and i curious about how those one save immunity are.
How strong if there is a thing that has will save immunity or reflex save immunity?
Is will save immunity need +2 LA by this alone?

[Khedrac]

First off, undead and constructs are not "immune to any effect requiring a Fortitude Save" - they are 'immune to any effect requiring a Fortitude Save that does not also affect objects' - this is quite a key difference.

Fortitude-based saving throws tend to be Save or Die effects so this stops a lot of "instant-kills" from being a potential issue - some work though, e.g. Disintergrate, though that is far form a guaranteed "Kill".

Reflex-based saving throws tend to be "save for half damage" effects - so improved evasion usually counts as immunity (imp. ev. is usually found on creatures with a high reflex saving throw, so it's common for a natural 1 to be their only fail).

Will-based saving throws are the most complex. Usually they are some form of "save or lose" (if only "save or suffer large penalties").

In my experience saving throw optimisation is Fort > Will > Reflex. If you fail the fort it is usually game over, while if you fail a relex it is usually time to call for the medic.

So - Level Adjustment effects? - I don't know, but I would not price Reflex that high - fluff-wise I would expect it to apply to entities that are very mobile, so it is really just a small step up from Improved Evasion which they may already have.

[Vaz]

What? Undead and Constructs Fort Save immunity is only partial - if a Fort Save effect can affect an object, then the Fort Save must still be taken - and usually at a massive disadvantage thanks to the lack of a Constitution score. The other ability to get this is Mettle.

Reflex Save immunity is less effective. Not only is evasion easier to get hold of, but there are less effects which are reliant on a reflex save failing - usually it is mostly "just damage" you're saving against.

Will Save immunity is part way available by becoming an Undead, Construct, Plant, by virtue of immunity to Mind-Affecting. Most (if not All) Mind-Affecting spells are Will Saves. There is also Mettle, which is harder to get than Evasion, and there's no Improved Version either. However, there are some Will Saves which are not Mind Affecting, neither do they have reduced effect from half saves, so Mettle is less useful in that regard.

If I was to judge it, depending on what other abilities came from it, a LA+2 template, maybe +3 depending on what else would be just right - although I still wouldn't take it. It would have to possibly have Evasion as well as scale, into something like Improved Evasion etc at later levels, and maybe give all good saves (LA+3 at least for the last one).

I'm not judging this off previous templates, like Half Dragon or Half-Field or whatever, as they're extremely underpowered, but rather what I feel is a bit more balanced.