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.
Your character is displayed as a trophy on a board. Other character trophies are grouped together over images of stages, which show where you'll be fighting. Depending on which group you choose to fight, you'll take part in anything from 1-on-1 matches, to 8-player free-for-alls, to team battles in which you can team up with characters you've defeated. If an enemy trophy has an icon of a trophy or a custom part on it on the board, defeating that character will earn you whatever they're carrying. On top of that, before each match, you'll have the opportunity to stop a slot, which will determine another prize you'll earn for winning the match.
The first three rounds are against normal characters. Your "Rival" will be in play, marked as a blue trophy. You can fight your rival whenever you want, and you'll have to fight them in the third match if you didn't defeat them already. The later you fight them, the more difficult they'll be, but the better the prizes they'll drop.
The next two matches are against alternate versions of characters. These trophies have black bases and alternate costume colours. These characters can have custom special moves, but are otherwise similar to the first few matches.
Before any of these matches, there is a random chance that an "Intruder" will drop in. This will mean one character will be replaced by a giant or metal character that's more difficult to defeat. Some of these matches may also be team battles, in which case you'll have to choose one or more partners from the characters you've already defeated.
The sixth round is against the Fighting Mii Team. You'll be attacked by a large group of very weak Mii characters that are easy to knock away with a single hit. This round is similar to one of the Multi-Man Smash minigames.
The seventh round is the boss round. Who you fight is determined by the difficulty level.
You' fight Master Hand on any difficulty level. 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. Crazy Hand will show up on Intensity 3.0 or higher.
- 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 7.0 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 form only exists in the Wii U version of the game. On 8.0 or higher, defeating Master Shadow will cause the Master Fortress to appear, along with a special heart container that will completely restore your health. Master Fortress is more of a level than a boss. It's a huge black dungeon full of enemies from the Smash Run mode on 3DS, and weak points. Your goal is to find the four glowing red weak points and destroy them, without getting KO'd by the enemies. There are Danger Zones, like in the Great Cave Offensive stage, except they're all yellow instead of red. You'll have to deal with the following enemies:
- Geemers: These Metroid enemies crawl along surfaces and don't really do much. They're the least threatening enemies here.
- Stalfos: Skeleton knights from Zelda. They're carrying shields and are tough to damage from the front, so roll behind them to attack them from behind.
- Plasma Wisp: From the Kirby games, these things can fire small or large plasma projectiles. They travel in a straight line so they're not too tough to avoid.
- Lethinium: These are the real killers. They fire energy beams that pass through walls and floors. They can fire these in any direction and sweep. If you see a Lethinium, defeat it as soon as you can.
Enemies are defeated after taking enough damage. It's a good idea to KO every enemy you come across, but especially the Lethiniums. Those are a pain. You can knock enemies into danger zones to do heavy damage do them, but definitely avoid them yourself.
The first weak point is directly inside of the Fortress. It's a linear path. After destroying it, the path to the second weak point will open up near the entrance, so backtrack to it. Watch out for the danger zones, including the yellow liquid at the bottom. After the second weak point, you'll be ejected back to Final Destination, so head back inside and back to the second path, which has now changed. You'll come across the third weak point soon. Backtrack from the third one and you'll see that another path (with a danger zone in it) has opened in the floor. Be careful and drop down. There's more yellow nastiness here. Destroying the final weak point will eject you back out for the final, super easy phase.
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 it survives 45 seconds without being KO'd (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. You can use the items that float in on balloons to help you out. You won't be hurt by explosions from bombs, and if you accidentally fall off the stage and die, there's no penalty. You'll just respawn. 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.