Although amiibo can always be left vanilla, the option remains to equip them with stat increases and bonus effects. In Super Smash Bros. Ultimate, amiibo can inherit Spirits to increase their Attack and Defense and add unique Spirit effects. In Super Smash Bros. 4, amiibo can be fed custom parts to increase their Attack, Defense, and Speed; they can also inherit bonus effects to add specific strengths to their arsenals.
In both Super Smash Bros. 4 and Super Smash Bros. Ultimate, once equipment or a Spirit is given to an amiibo, it cannot be recovered (even if the amiibo itself is not saved afterward). Both equipment and Spirits must be obtained by playing single player modes. Custom parts can be collected from Master Orders or Crazy Orders in Super Smash Bros. for Wii U (or Trophy Rush on Super Smash Bros. for Nintendo 3DS); Spirits serve as rewards in World of Light or the Spirit Board in Ultimate. Furthermore, both equipment and Spirits can be received as gifts after training an amiibo and scanning it in the amiibo menu.
In Super Smash Bros. 4, an amiibo’s Attack, Defense, and Speed can all be increased by equipment. An amiibo’s stat total cannot exceed 120; each stat can be raised up to 200 or brought down to -200. It can also utilize three different bonus effects, some of which did not return in Super Smash Bros. Ultimate.
In Super Smash Bros. Ultimate, an amiibo’s Attack and Defense (and not Speed) can be enhanced with Spirits. Unlike Smash 4, an amiibo’s maximum stat point total decreases if it uses Spirit effects. With no Spirit effects, an amiibo’s maximum stat total is 5000; with all three slots filled, the total is lowered to 4200. Some Spirit effects occupy more than one slot; for example, Armor Knight occupies two slots and Super Armor occupies all three.
In Super Smash Bros. 4, equipment setups were generally more balanced (60 / 60 0) but often sacrificed Speed in favor of additional Attack and Defense increases (100 / 100 / -80) on characters with reliable recoveries. In the early Smash 4 amiibo metagame, fighters almost always ran a defensive-heavy spread (40 / 70 / 10).
Within weeks of Super Smash Bros. for Wii U’s release a viable setup was brought to light by Amiibo Trainer. It was known as the Rock-Paper-Scissors build, and consisted of Critical-hit capability, Explosive perfect shield, and Improved escapability. It is to this day considered the most powerful setup for an amiibo in Smash 4; however, Critical-hit capability and Explosive perfect shield were soon banned. In the late Smash 4 metagame, most amiibo ran Auto-heal capability, Lifesteal, and Improved escapability. Other viable bonus effects included Improved launch ability and Hyper smash attacks.
In Super Smash Bros. Ultimate, Spirit setups tend to be fairly defensive; this is because Defense points scale to higher values than Attack points. As a result, many amiibo run a fully defensive setup (0 / 4200) while others run a more balanced one (2100 / 2100).
Statistically speaking, Super Armor and Slow Super Armor are the most powerful Spirit effects in the game and are especially effective on heavyweights; they were banned from the Spirits metagame within two weeks of Ultimate’s release due to their overcentralization. With the removal of Super Armor and Slow Super Armor, Armor Knight soon became the centralizing Spirit effect; in fact, it is considered mandatory on almost every character and is run almost exclusively alongside Move Speed ↑.