Now that Dr. Mario World is out and players are going to be diving into the game, one of the more important things to do is to link your accounts to Dr. Mario World so that you can access the benefits of connecting to your friends, most importantly so that you can send them hearts and they can send you hearts. Both you and your friends can also request hearts from each other in the event that you didn't get any from them on days you log in to play.
With Dr. Mario World and like most games available on mobile you can link your accounts so that you can play with your friends who you are connected with through that account. For example, if you connect your Facebook account to the game then you would be able to see any Facebook friends who also play Dr. Mario World and you could then interact with them by sending each other hearts which is the game's energy item for playing a stage, as well as play against them in versus mode.
Initially you can only link your Nintendo account, and to do that you will first have to make your way through the tutorial. Once you can access the settings menu, tap on the settings icon and the red button labeled Back Up Save Data.
After tapping on this button a window will pop up alerting you that you can link your Nintendo account and that this is what you'll need to do if you want to be able to back up your game progress. This is highly recommended if you don't want to lose your progress.
As a side note, if you link your Nintendo account, and then have to uninstall and reinstall the game for any reason and then try to re-link your Nintendo account, you may be met with an error code that tells you you aren't able to link your Nintendo account to Dr. Mario World. If this happens, you will need to delete any game save data that may have, before you can re-link your Nintendo account, but it's important to know that this will also mean you have to restart the game from the very beginning and you will lose any progress as well as purchased items, such as premium currency.
To delete your game save data, simply open the settings menu and tap on the About Game menu. Here you will find an option to delete your save data, which will allow you to re-link your Nintendo account, or link the game to a different Nintendo account if you wish.
You won't be able to link your Facebook or LINE accounts until you have unlocked versus mode, which you cannot do until you have beaten the first 20 stages. Once you have unlocked versus mode, go back to the settings menu and tap on the blue button next to the one you tapped for linking your Nintendo account, which will allow you to link your Facebook account to the game.
After this point you'll be given a window popup that will ask you to confirm that you want to link your Facebook account.
For linking LINE, you will need to tap on the Friends button in the navigation bar at the bottom of the game's UI. Here, you can see a three dot button that when tapped will allow you to link your social accounts for playing with friends, which includes accounts for Facebook and LINE only as previously mentioned. It should also be noted that to invite your Facebook friends to play you will have to hit the "link" button for Facebook from the Friends page as well to login.
After all these steps that's pretty much it and you should be set up with your Nintendo account for backing up save data, and your Facebook and/or LINE accounts for playing with friends. Keep in mind that save data can only be backed up to your Nintendo account and not Facebook or LINE, so you will need to either create one or link an existing one if you want to save your game data. Now that your accounts are linked, get your friends playing so you can face off against each other in versus mode!