[It's voice ]

"Its" is possessive. "It's" is short for "it is".

[ it's all I have left of mother ]

When used in place of a name, it's capitalized like one.

[Despite her friendliness I can't help but feel uneasy. Can you really trust a Ghost?]

You really haven't explained why your character is so afraid of ghosts in general, actually. The ones actually around threatening him seem there on specific orders, not because the type normally likes to suck out the blood of any pokemon they catch.

You wouldn't capitalize animal or mouse or dragon, so you shouldn't capitalize words like pokemon or pikachu or charizard. The only time you should capitalize it is if you're using it as the pokemon's name, ie, Ash's pikachu is called Pikachu. This is because you only capitalize when it's a proper noun, which are the names of places or things. Similar reasoning should be applied to any other words you're thinking of capitalizing, like telephone or trainer. Or professor.

[Ghost's can sense fear, and I'm pretty sure a Sneasel would spot movement before I could get to deeper water.]

Never use an apostrophe for a plural, and this sounds like you mean the sneasel are working with ghosts, but that really doesn't make much sense as a partnership.

[wouldn't of ]

Wouldn't have.

[ Mahogany town. ]

You have to capitalize both halves of a name.

Your character is rather unlikable. He just fled desperately to escape attackers, but upon realizing he left his brother behind, he doesn't panic and rush back out to find him. He doesn't even feel guilty he didn't realize his brother was missing. He just says his brother's probably hiding somewhere else and swims deeper. Then he goes to find something to eat, planning to not even try to find his brother until the morning.

This is pretty good. Your descriptions are excellent. I really like the suspense here. I'll follow this