I'm sure I don't need to tell you this, but starting with Scales of Thoth is extremely powerful, almost overly so. It's pretty much a guaranteed +1 to everything since the cost for the Scales is minor in comparison. Now, you do have it placed on a character that optimally uses Scales as a 4/4 character, but the main reason Scales is so powerful is due to the accessibility of it during any phase. All that being said, there's nothing necessarily wrong with having a character that starts with Scales, but it does usually become that character's defining trait.
In relation to his story, Scales is basically an absolute fail safe. It's literally impossible to fail your personal story with Scale of Thoth since if you would ever be in a position to fail, you can use Scales re-actively to avoid meeting the criteria of the failure. Additionally, the pass condition is actually pretty easy. Anna Kaslow is most frequently seen on Independence Square, so you can get yourself to five clues and then just sit on Indy Square having encounters. Eventually, you will either have an encounter with Anna Kaslow or you get sucked into a gate while holding 5 clues. Alternatively, you can see which allies are available at the start of the game and if Anna Kaslow isn't available you just ignore your personal story altogether.
Okay, maybe it's not actually that bad, but it is a little too easy. I would recommend changing the fail condition to be something a little easier to fail.
His main ability is fine since it only allows you to use leftover movement points and you can't use it to pick up extra clues or take extra encounters. However, it can be a little strong if he can still fight monsters during the extra movement given that he's a 5/4 on fight and will, and is effectively a 6/5 with Scales factored in. Also, what happens if a monster ends his movement the first time? Does he get to move again on the second movement phase?
I'm sure I don't need to tell you this, but starting with Gruesome Talisman is very powerful.
Okay, I'm mostly joking. Mostly. Gruesome Talisman is actually quite strong as a starting item since it allows you to max your fight in most combat instances without having to worry about horror checks nearly as much.
Ovi is an incredibly flavorful character. The combination of terminology, manipulation of "occult" entities and starting with the most voodou of items (Gruesome Talisman) all really helps set the right tone here. I kind of wish his ability did more though, right now it feels like the Gris-Gris of Legba is only helping investigators deal with gates to the other worlds, not the other worlds themselves. I kind of feel like it should be closer to Jim Culver where it manipulates the other worlds into having an extra color available. But, whatever you choose, I do feel like it's not really doing much right now, ESPECIALLY for it's current price.
Pass Condition should say "If there are sanity tokens on 2 different Other World locations". Here's some bad news you might not like to hear though:
I don't think anyone that plays this character is going to use his ability outside of some dire circumstances, and I'm pretty sure they'll just ignore the personal story. So you need to toss 2 unique items at the end of 2 different Other Worlds without sealing at least the first of those gates, all for the ability to slightly adjust monster movement. You fail if you ever seal a gate, which is usually something you want to be doing, and the price of failure is...pretty much nothing. In fact, if you never discard any unique items and seal every gate you can, his failure actually doesn't do anything.
I think that if you found a way to make his main ability a little more enticing, it would encourage people to want to use it more, which will in turn encourage players not to fail his personal story.