The controls are largely customizable in the settings menu. Super Smash Bros. is a bit different from most fighting games, so take some time to familiarize yourself with the controls if this is your first Smash Bros. game.
Basic Movement - You move using the circle pad. Move left or right by moving the circle pad normally, or move it quickly in either direction to dash. Attack while dashing to do a dash attack. Hold down to crouch. Some characters can crawl.
Jumping - By default, you can jump by pressing up on the circle pad, but you can turn this off. You can also jump with X or Y. You can jump a second time in the air. Some characters can jump even more times in the air. If you land on a character's head (either in the air or on the ground) you can press the jump button to leap off of them. You can do this up to four times before touching the ground, jumping a little lower each time. Most characters can "triple jump" by pressing up and B at the same time. While in the air, tilt the circle pad down to drop faster.
Basic Attacks - Press the A button to do a quick, weak attack. For most characters, pressing it repeatedly will unleash a basic combo. Some characters have different combos depending on how fast you press the button. Press it in conjunction with a direction to attack in that direction with a bit more power. You can also attack while crouching or in the air. Aerial attacks can be aimed in different directions for different effects, too.
Smash Attacks - Press a direction and the A button together quickly to do a smash attack. This type of attack does lots of damage and launches enemies far. You can smash attack forward, up, or down, with different results. Hold the button to charge your smash attack to do even more damage and send your opponent flying farther.
Special Attacks - Press B to do a special attack. Each character has four types of specials by combining the B button with different directions on the circle pad. These have various effects that differ from character to character. If you're holding a Smash Ball, you can do your Final Smash by pressing B.
Shielding - Press R to raise your shield. This is a barrier that will gradually shrink with time or as it takes damage. Stop using it to recharge it. Smaller shields will cover less of your character's body, but you can aim them by moving the circle pad. If your shield breaks, you'll be stunned, and you won't be able to move for a while. You can't shield in the air. If you press the Shield button just as the attack connects, you'll Perfect Shield, meaning you can recover faster. Shields don't protect against grabs, so grab a foe if they're guarding too much.
Rolling and Evading - While shielding, quickly press left or right to roll in that direction. You'll pass right through enemies and attacks this way. At the end of your roll, you'll be facing back the way you came. Press down while shielding to quickly evade an attack without moving. Press the shield button in the air to evade in the air.
Recovering - If you're knocked into the air, or damaged while you're in the air, hit the guard button as you hit the ground to quickly bounce back. If you're knocked onto the ground, you can roll by pressing a direction, or attack as you stand by pressing the attack button.
Grabbing - Press A while shielding or press L any time to grab an enemy. Some characters can grab from a distance. While holding an enemy, you can attack them with A or throw them by pushing a direction. Down throws won't send enemies very far, but they will leave them open to follow up attacks. Grabbed enemies can break free by moving the circle pad and pressing buttons, but they'll have a harder time if their damage is high.
Taunting - Press the dpad in any direction to taunt. This is mostly just for show.
Ledge Grabbing - If you touch the edge of the stage from below, you'll grab onto it. You'll be invincible for a moment when this happens. From here, you can jump, climb up, or attack, by pressing the corresponding buttons.
Items - Pick up items with A. Some items will be used automatically. Some are for throwing, and can be thrown with A. Pick the direction with the circle pad, or quickly move the circle pad and press A at the same time to throw the item with more power. Some items are for swinging or shooting. Press A to do this. Swinging items can be smash attacked. Drop an item with L, or throw it the same way you throw throwing items, except with L instead of A.
Screenshots - Pause the game and press L or R to take a screenshot. Screenshots are saved to your 3DS SD card and can be viewed in game or in the 3DS camera app. Press X or Y to zoom in or out while paused, use the circle pad to rotate the camera, and use the dpad to pan the camera. You can automatically focus on a character by touching their icon on the bottom screen.