Classic mode is the standard arcade-style gauntlet that has been in the series since the beginning, when it was the main single player mode. Clearing Classic mode will earn you a trophy of the character you used to clear it.
Before starting, you'll be asked to choose an Intensity. The default is 2.0, but you can raise or lower it with coins. The higher the intensity, the tougher the enemies, but also the more coins, trophies, equipment, and custom specials you'll find. Before each match, a slot will spin, which you can stop to see what kind of prize you'll get for winning. This can be coins, trophies, or custom parts/costume items of different quantities. If you want to cheat, you can bring up the Home menu on your 3DS to pause the slot, and, if it's on something you like, hold A to return to the game and immediately stop the slot. Keep in mind that the slot will stop on whatever item will be in the centre next if there's no item currently perfectly centred. This means that if an item's icon is even a tiny bit lower than the centre when you press the button, it will move past and you'll get the next item instead. If you lose a match, continuing will remove some of the items you've won, in the order in which they were obtained. It will also lower the intensity, making the game easier and reducing the prizes you can earn.
Before each match, you'll come to a fork in the path where you can decide which way to go, determining who you'll fight. You can tell by the icons which game your opponent will be from, but some characters share icons so it's impossible to tell 100% a lot of the time. Red paths are a bit tougher but you'll find more coins on the path leading to the match.
You'll have to fight a five matches with different conditions. Some will be regular one-on-one battles, some might be free-for-all or team battles, and some are a bit different, where you have to fight giant characters, permanently metal characters, or a hoard of weak Miis. All matches are one-stock, except you're a special little snowflake so you actually get two stocks. This is probably so you have a safety net in case of something like a bob-omb spawning in front of your Falcon Punch.
After clearing those five, you'll have to fight a boss. Bosses can't be knocked out of the ring. They have a set amount of HP which you'll have to whittle away, and they'll be defeated when it runs out. Master Hand is always available, but if you're playing on 3.0 or higher, you'll be be able to switch paths and fight Crazy Hand as well. (You are free to stick to the main path and fight Master Hand alone, provided you're playing at Intensity 7.9 or below.)
There is a challenge to beat this mode on intensity 9.0 "or higher." 9.0 is as high as it goes, but anyway. I did it as Charizard, because the final bosses are the toughest part, and he is a destroyer of bosses with his Rock Smash. Use it "inside" of enemies to do tons of damage. You can use custom characters, as well, so if you want to beef someone's stats up with equipment, that is an option. Keep in mind that it will make the final form more difficult, though.
These boss names are official, but the names of the attacks listed here are not.
Master Hand will return to the right side of the stage between attacks. Hit him with powerful aerials or, if they'll reach, upward smash attacks.
- Finger Snap Snaps its fingers and stuns you if you're on the ground. Keep your distance to avoid this, or simply guard if your shield is strong enough.
- Side Punch Punches across the stage. Likes to combine this with Scurry.
- Back Punch Move into the background and punch forward like a rocket. Air dodge or roll.
- Finger Guns Fires bullets from its fingers. Can't be absorbed but can be reflected. Roll or air dodge to avoid. Can also just block it if your shield is strong enough. It'll shoot one or three blasts depending on how much HP it has.
- Platforms Will throw square platforms onto the stage that will rise into the air and carry you away if you're standing on them. You can avoid these pretty easily by simply double and triple jumping just off to the side of the stage. Hanging off the edge works too.
- Finger Walk Walks along the stage on its fingers. It will flick you if you get too close. Roll right past it when it gets close to dodge, or just double jump over it.
- Fireball Throws a fireball into the air and then grabs it, breaking it into smaller balls that rain down on the stage.
- Fan Waves fast to blow an icy wind at you. The wind carries ice chunks that will freeze you if they touch you. If your character is good in the air, float just below the edge of the platform on the right side. Otherwise, hang off the left edge and hope for the best.
Crazy Hand's attacks are... well, crazier than Master Hand. Like his northpaw sibling, he'll return to his side of the stage (the left) between attacks, and will be open to aerials or smash attacks.
- Scurry Scurries along the ground. Jump over it.
Bomb Rain Drops a flurry of bombs straight down. They explode, of course. Just stand back and let it happen.
- Slap Slaps across the length of the stage. Air dodge or roll.
- Black Hole Tear a hole in the background and reveal a black hole that will suck you in. Keep your distance!
- Pillars Jams glowing poles in the ground. These will explode if you touch them. They're equally spaced so stay between them until they disappear. You can roll past them with some skill.
- Finger Lasers Lasers come from each of its fingers and sweep the stage. Try to stay in the air to avoid this, since it's tough to dodge if you're in the fray.
- Energy Ball Tosses a ball into the air, then back into the hand, before slamming it down on the ground. Probably won't hit you if you're not near the centre of the stage, especially if you're in the air.
- Flail Lays in the centre of the stage and flails around, causing an earthquake. Just stay back.
- Grab If one of them is floating close to you and not doing anything, it's about to grab you. Air dodge or roll to avoid this. If you get grabbed, move the circle pad and press the buttons to break free. Be careful not to accidentally Rollout off of the stage due to mashing.
- Palm Punch Master Hand beckons Crazy Hand over. Crazy Hand will punch across the length of the stage and land in Master Hand's palm. Easy to jump over.
- Palm Punch? - Crazy Hand beckons Master Hand over this time, and Master Hand will zoom across the stage at a downward arc, but instead of catching him, Crazy Hand will scurry across the stage immediately after.
- Drill Spin up into the air and come straight down to drill you into the ground. Roll out of the way at the last moment. This can still suck you in if you touch it while it's spinning. This attack will only land over solid ground, so if you're floating off to the side of the stage, you're safe.
- Spike One hand throws energy balls and the other slaps them down. The small balls are easy to dodge in either direction. Dodge the large ones by rolling in the direction of the hand that is smacking them down.
- Rocker Gesture I don't know what else to call this. Extends its middle finger, pinky, and thumb, and rockets off into the background before swooping back in to hit you. This is pretty easy to air dodge if you time it right.
- Down Punch Punches straight down. Roll out of the way at the last moment or air dodge. You can attack Master Hand briefly after it lands. Crazy Hand will smash the ground a couple of extra times. This will only land on solid ground and won't hit you if you're hovering off the side of the stage.
If you're playing on 5.1 Intensity or higher, both Hands will leave after taking enough damage, and you'll have to fight a brand new boss: Master Core. Master Core has several possible forms, and will be tougher at higher Intensities. The number of phases this fight has depends on the Intensity you're playing on.
Unlike the Hands, Master Core does an attack and then stops for a moment. This means you can focus on dodging their attack and then immediately counterattack before going on the defensive again. Master Core doesn't technically have an HP meter. It's surrounded by a black "swarm" that gets whittled away as you damage it. The higher the difficulty, the larger the swarm, and the more damage it takes overall. It is essentially identical to whittling down the HP of the Hands, just harder to read because there's no number.
The most threatening of Master Core's forms, he only appears at 7.5 Intensity or higher.
Bomb Tumour: A giant tumour appears on Master Core's head. He slams it to the ground (or on top of you if you don't move) and projectiles fly out and hover in the air. These explode in the air like X-Bombs. They always explode in crosses, so get in a safe position. Ideally, you'll be able to get near Master Giant and get a few hits in while they're exploding, but it's safer to do a well-timed jump above the explosions, but obviously not directly above a bomb.
- Scream: Grabs his head and lets out a scream that sends you flying.
- Swipe: Swipes across the ground. The swipe doesn't actually do anything, but a follow up slash quickly occurs a moment later. Time a roll towards Master Core to dodge the follow up. High launching power.
- Headache: An X appears on his head and sucks orbs of energy in from off screen. Can suck you in, too. When he starts drawing you in, quickly roll away to get a bit of distance, but don't continue rolling madly as you might instinctively want to do. Instead, wait for the orbs to appear and roll past any orb that is about to hit you. This will let you avoid the orbs and build more distance at the same time.
- Lift: Fires energy balls into the air and then lifts the stage up under you to bring you up to them. If you're not on the stage at the time, it's likely to meteor smash you when he brings it back down.
- Arms: You'll know this attack is coming because his head glows red. Master Core grows an extra pair of arms and sweeps them across the stage. Can grab you and pull you in, damaging you. One of them moves in one direction across the stage and the other moves in the opposite direction above the stage.
This form is quicker than the Master Giant form, so you'll want to play more defensively. Get close and dodge his attacks, then strike back before he readies another. You'll have to fight this form after defeating Master Giant, or at Intensity 6.0 or higher.
- Spikes: Stomps on the ground and spikes come up beneath you. You can tell this is coming when spikes stick out of his back first.
- Bite: Head moves into the background and comes forward and bites you. Roll or air dodge at the right moment to avoid this.
- Leap: Leaps into the air and slams down on one of the corners. This causes the entire arena to tilt momentarily
- Dark Thunder: Calls down a dark thunderbolt that strikes Master Core and will damage you if you're close enough.
This form has a wide attack range and can attack from different angles thanks to consisting of multiple parts. Hit any part of it to damage it. This form shows up at Intensity 5.1 or higher, or after defeating the Beast form. Peach's Peach Bomber is pretty incredible against this form.
- Slash: Does a simple upward slash. Will flash when he's about to do this quick attack.
- Projectiles: Slices and throws either one or two sets of two energy balls that move across the screen, either in a straight line or more erratically. Watch out, they come back the way they came. Ness can absorb these with PSI Magnet. If there are only two balls, they will be larger than if there are four.
- Surrounded: Breaks apart into a set of swords at various spots. Each one attacks towards the centre before the large one slices down towards the player. This will aim for you, so dodge it.
- Flurry: Catches you in a flurry of strikes and then one large vertical one launches you. This is actually pretty easy to block with your shield.
You'll have to fight this after defeating Master Edges. Master Core turns into a huge copy of your character, complete with any customizations you've made to them. The more you damage it, the smaller it will get. Obviously the strategy for dealing with this differs from character to character. It still goes down after taking enough damage, but you can knock it out of the ring to KO it, too.
This isn't a real form so much as an easy, satisfying reward for making it through the other forms. This orb, now free from darkness, just sits there waiting for you to give it a few good, hard smacks and send it flying out of the ring. Oddly, if you wait 45 seconds without getting a KO (which would almost have to be intentional) it will pulsate and explode, possibly knocking you out with it. You'll be ok if you have a stock left, though.
The credits feature a minigame you can play to earn some extra coins. As the names scroll towards the top of the screen, attack them to send them into the background and into the frame. This will gradually reveal a picture of your character. You'll actually have to aim, standing or jumping in front of empty spots and attacking names to smash them into places that need filling. When an empty spot is small enough that it might be difficult to see, it will start to sparkle to make it easier to find. Fill in 100% of the image and you'll earn 100 coins. If you fail to complete it fully, you'll still earn some coins. You can skip this minigame by pressing start.