The sonar thing could work very easily. Normal humans can be taught to echolocate effectively; blind people can be taught to do it quite readily as their brains process information in a different fashion. (brain plasticity is fascinating; for instance there is intense activity in the visual centers of a blind person when they read braille) That someone could be born with hearing developed to that point is not a large stretch at all.
Infravision, however, is tougher. Infravision would not stem from natural mutation, but rather it would require a long time of evolution. Since infravision is heat sensitive, the heat of the head that held the eye would flood the eye and it would need cooling. I once read a long and intelligent article on explaining infravision in the D&D world, and surprisingly it brought up these and other intelligent points. Anyway, creatures that see in the dark in the natural world do it by other means, usually they have more sensitive eyes. Cats have specially formed eyes to collect a lot of light. Dogs have 25% more light sensors than color sensors.
I could see a few "Mutation" traits like this:
Feline Eyes: Your eyes have the light-focusing characteristics of a cat. You have 25% better night vision.
Hypersensitive eyes: Your eyes have developed to an extreme level. You see 65% better in darkness, but are hampered by bright light and sunlight especially, taking 25% penalty on all vision-related actions in bright light. Perhaps you can find a way to alleviate this penalty? [Mirrored shades, anyone? Another use for this item, presuming it returns!]
Echolocation: Your auditory centers are liked unusually with your visual centers. You can sense objects with sound, and are never truly in the dark. In total darkness, you can still "see" as if in dim light, and you take only half penalties from blinding effects and eye damage. You also get +1 on auditory PE checks. However, since you rely upon your ears for this orientation, you take equivalent penalties to vision-related tasks if you are deafened.
Infravision, however, is tougher. Infravision would not stem from natural mutation, but rather it would require a long time of evolution. Since infravision is heat sensitive, the heat of the head that held the eye would flood the eye and it would need cooling. I once read a long and intelligent article on explaining infravision in the D&D world, and surprisingly it brought up these and other intelligent points. Anyway, creatures that see in the dark in the natural world do it by other means, usually they have more sensitive eyes. Cats have specially formed eyes to collect a lot of light. Dogs have 25% more light sensors than color sensors.
I could see a few "Mutation" traits like this:
Feline Eyes: Your eyes have the light-focusing characteristics of a cat. You have 25% better night vision.
Hypersensitive eyes: Your eyes have developed to an extreme level. You see 65% better in darkness, but are hampered by bright light and sunlight especially, taking 25% penalty on all vision-related actions in bright light. Perhaps you can find a way to alleviate this penalty? [Mirrored shades, anyone? Another use for this item, presuming it returns!]
Echolocation: Your auditory centers are liked unusually with your visual centers. You can sense objects with sound, and are never truly in the dark. In total darkness, you can still "see" as if in dim light, and you take only half penalties from blinding effects and eye damage. You also get +1 on auditory PE checks. However, since you rely upon your ears for this orientation, you take equivalent penalties to vision-related tasks if you are deafened.