Interesting Ethereum wallet tricks thread

I have been lurking around in this sub and every now and then I discover something interesting related to ethreum wallets and some tricks I never thought existed/were possible. For example yesterday I didn't believe at first the 25 words secret phrase. There is also the ethereum dapp that makes you login as any address(it's a fake login ofc) So I'm making this thread to allow anyone with another cool "trick" to share it here so we all get to know it. A short description of how it works will be appreciated as well.