Yup, seconding this. It’s 100% legal to make a game with the same basic mechanics if you don’t use the same name, textures, specific character designs, etc–all the trademarked & copyrighted bits–but if you do you can expect a Cease & Desist if the game ever gets big.
(also not a lawyer, the above is not legal advice, if you have legal concerns contact a professional to be sure)