Actually both water abilities are useful. I played a water specialist.
While the bonus abilities give more senses in general, only the regular mirage lets you get tactile sense. Plus the intent is that if you take mirage and get a sense you can get it earlier, but you get less and not as many benefits.
Plus mirage has a LOT of things it can add to, range, DC, senses, etc.
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On a side note it was mentioned in the other thread and suggested to be moved here.
Hollow Within feat. Look at that save and tell me how it makes sense. Level+charisma bonus? first it is so low you will always make it no matter what level. second, why are you punished for having a higher stat?
Normally higher stats HELP your saves, not hurt them. So it doesn't make sense and the save DC is too low, imo.
Edit:
As mentioned in the other thread, barring natural ones a character with a good will progression rate.
Level 1? Auto-make it.
Level 10? +7 minimum (zero wisdom) to a DC 10. You'll make it
Level 15? +9 minimum but WBL will let you get magic items that boost it making a DC 15 stupid easy.
Level 20: DC 20. You have a minimum +12, plus magic items. If you can't make a DC 20 by level 20 you aren't TRYING. Especially when it only activates when you get dropped.