There are lots of good reasons to own Splatoon amiibo, but these two in particular are very special.
If you didn't play the original Splatoon, the names Callie and Marie might not mean much to you. The infamous Squid Sisters were the face of the original game, which was so popular in parts of the world that a hologram concert was held with these two as the stars of the show. In Splatoon 2, Callie and Marie take a backseat to two new pop stars on the big screen in the middle of downtown Inkopolis, but for a good reason. They're now a big part of the Single Player missions, complete with plot twists all its own.
That's where the amiibo for these fresh little squids come into play, and when you beat the game, it becomes clear you've invested well by having these two figures nearby.
If you try to use the Callie or Marie amiibo without beating the core game, you'll be met with a pair of notes explaining how busy these two superstars currently are. Clear all of the levels in each of the five areas of the story, and you'll unlock the ability to use these two amiibo. Like every other Splatoon-themed amiibo, you can save your settings to these amiibo so you can quickly switch between your preferred weapon and armor loadouts. Also, you'll be given a piece of armor with the promise of more armor as you continue to play the game.
That's where things get fun.
These "replica" sets are unique to Callie and Marie and only available through these amiibo. The head gear you get at first is styled after the armor for the single player missions, and you can unlock torso and foot gear to match as you play. Especially for early players, this gear kit can give you a considerable advantage.
Callie will give you the Hero Jacket Replica, Hero Headset Replica, and Hero Runner Replica pieces, which include Swim Speed Up, Run Speed Up, and Quick Super Jump abilities when these items are equipped. You start out with just the headset, but Run Speed Up is not easy to get early on and can give you a big advantage in close matches.
Marie will give you Armor Jacket Replica, Armor Helmet Replica, and Armor Boot Replica pieces, which include the Special Charge Up, Tenacity, and Ink Saver abilities when the items are equipped. Tenacity, the ability that comes with the Armor Helmet, makes your special ability charge much faster when your team has fewer active players than the other team. This means when it seems like your side is at a temporary disadvantage, you can quickly level the playing ground.
These are far from the best sets you can get in the game, but they're easily some of the best sets you have access to until you're a much higher level. If that's something that appeals to you, pick up these amiibo ASAP and make sure you've actually played through the story!