I would recommend making a character to write with. See where it says "Show Bio" next to people's names? In the About Me section of your profile, you can write down what you want to be shown there. I'd say about 85% of the people here use that for a single character, making different accounts for each. There's been a little trouble with that recently, so what I've always preferred to do is make links to character bios. If you click mine, you'll see a list of dudes I've made to write with. It's common to change your avatar to the look of the character you're currently using.
There are two major rules on the Vine, and those are to avoid things called God-modding and no-selling. God-modding is when you take an action that could be prevented by another character, control another character, or alter major canon without permission. If you say your character kills another player's, well, you can't really do that. Basically, everyone determines exactly what happens to their own character.
No-selling is when you refuse to take any hits. If your character dodges, shrugs off, or just generally tanks everything that comes their way without at least acknowledging the attacks of their opponent, it becomes incredibly unfun to write with them. This is why, in my opinion, it's easier to write with characters around Spider-Man's power level. Healing powers are also nice (and common) because they let you sell a hit without long-term consequences.
Suggestion: You're off to a very good start with your character Achilles, but I'd recommend a way to "sell" other people's attacks. Absolute invincibility, while not against the rules, makes it hard for others' attacks to affect you (of course). People often won't want to fight someone they can't affect.