All of these things can be answered in cunningkitsune's guide, it's amazing, I really think you should check it out, but I'll answer some stuff.
Strengths and Weaknesses:
I'll break them down into concise pros and cons:
Pros:
- Agile
- Amazing vertical kill power
- Is a fast faller
- Best upthrow in the game
- Shine and ability to gimp
- Has a plethora of options in neutral
- Great kill set ups on a lot of the cast
- No bad matchups (worst is even)
- Great recovery, long as hell.
- Aren't limited to a specific style.
Cons:
- Is a fast faller
- His weight makes him total combo fodder, so fox is kind of a glass cannon at times.
- Everyone is basically good against fox, well not good, they just know fox and his options most of the time. The CPU people beat up the most and practice the most on is basically fox. People always seem to focus on fox for a lot of things (good and bad) Mang0 says it best when he says Spacies are like Rockstars. They're extremely well known, and can also go down pretty hard lol. (this applies to the combo thing too.
- Prone to getting gimped cause of his extremely predictable recovery. Ya really gotta mix it up when coming back.
- Requires a considerably large amount of practice time compared to the other cast, as a fox main you have to put your tech practice to good use. You don't have to be overly technical, but you have to know your tech still.
Upthrow follow ups, you should become familiar with those and at what percents they work on characters, aka like upthrow up air on spacies works at around 110, kills at around 130, it's a broader range than that but it's just the basics, it's also stage dependent.
The rest is all in Cunning Kitsune's fox guide, it's in the front page so please. Just look at it and absorb the info haha.
(He's got other pros and cons, I'm just too tired to state them, hope it helps
)
EDIT: Also, for "neutral" game and how to play it with him, it's really up to you. Look at how top players play, read around what people understand as the neutral game etc.
