2. Bitcoin Cash (BCH)last November 2017, touted as the "real Bitcoin" - FAILED
3. Ripple (XRP) - February or March this year, too decentralized - FAILED
It there's some coins that will topple bitcoin, its not yet created. Bitcoin has already gained the trust of the investors and no amount of FUD and fake news coming from different sectors or coins will simple stop Bitcoin. And I agree with @Pursuer, the only possible way to take the crown from bitcoin is that a coin that will have a real usage, but so far we haven't seen any, but shitcoins after shitcoins whose purpose is for pump-and-dump scheme.