For instance, MP IV into a Grimlock.
- Scenario 1: Not blind, no blindsight, no blindsense (since Grimlocks do not specifically have blindsense)
- Scenario 2: Blind, no blindsight, no blindsense
- Scenario 3: Blind, no blindsight, blindsense to blindsight range (40 ft.)
RAW seems to support Scenario 2. Is there any evidence I'm overlooking to favor Scenarios 1 or 3?
Scenario 2. A grimlock has no eyes, so the form you take on has no eyes. Since MP IV doesn't provide blindsight as one of its choices (for whatever reason), you can't see.
Personally, I would use scenario 4, granting blindsight even though the spell doesn't say it does so.
(I also think the lists of granted abilities seem pretty randomly assembled for most polymorph spells)
If it was my table I would probably go with #3.
There is some rules support for this: "In addition, each polymorph spell can grant you a number of other benefits, including movement types, resistances, and senses. If the form you choose grants these benefits, or a greater ability of the same type, you gain the listed benefit. If the form grants a lesser ability of the same type, you gain the lesser ability instead. (PFRPG 211)"
I would consider blindsight to be a greater ability of the same type as blindsense. Since it also states if it is lesser ability (such as the range in this case) you take the lesser. So, you get the lesser of the ability, blindsense, because of the limits of the spell and you get the lesser of the range, 40', because of limits of the form.
Maybe not strict rules-as-written but it fits my concept of rules as a framework.
That would be my view as well, a similar issue came up with the Cave Druid Archetype since oozes have no eyes either.