Using amiibo figures with Super Smash Bros. Ultimate is quite interesting. For one, scanning an amiibo figure creates a Figure Player (FP), which can battle against you. FPs learn and improve the more they fight, and a well-trained amiibo FP can put even a seasoned Smash player to shame.
However, there’s a hidden benefit to amiibo figures in Ultimate: scanning a figure you’ve used in the past grants you a series of gifts. These gifts include Spirit Points (SP), Gold Coins, Spirits, and even music tracks.
Simply go to the amiibo menu and scan an amiibo you’ve used before. A screen will pop up, similar to the one you’d see when you won a Spirit battle, which displays the loot you’ve received.
It seems like you can repeat this as often as you’d like, and as long as your FP has made progress between scans you should be rewarded. Even after you’ve hit level 50, it seems like your amiibo will keep racking up rewards as long as you’ve used the FP in battles.
Oh, and even scanning non-Smash amiibo figures will grant you in-game bonuses, but this is a one-time offer per figure. If you try to scam the system, you’ll see a warning message.
Oh well, it was worth a shot.