Two-Step Verification is a pretty simple concept that a few games with cash-shops and in-game purchases use that for if you account is hacked or stolen, that person is unable to access your various belongings without a secondary verification password.

This could be a 5-8 digit number or a unique password different from your mouse password, that would have to be entered if you wanted to access your shop or inventory during a login session.

The password wouldn't be required to be entered more than once per login session and perhaps could even have the option to save that IP that you're connecting from, so that it doesn't have to be entered in future sessions.
It'd be something that is optional, you'd get the option to pick if you wanted to have this extra bit of security or not, a small button in the shop could be added to change the verification or to opt into having it on your account.

People getting hacked in Transformice isn't a common thing and there isn't much, if anything to gain from hacking someone due to the verification needed to even spend fraises, but generally if someone has your mouse password, you're at a risk of them having your email as well due to the amount of players who commonly use the same password for everything.

Two-Step Verification just adds an extra bit of security to your account just in case you do actually get hacked and don't want to risk losing consumables or cheese that you have saved up.

/half-support The security on here is enough already. This is too much

Well that's why it's an optional thing, you're not required to have it, but for those that want that bit of extra security on their consumables or cheese have the option to have it.

/support
An optional option for more security on your profile is a great thing.