The Infinite Sword Glitch (commonly abbreviated to "ISG") Is a glitch which causes the hitbox of link's sword to remain in it's attacking state after the attack has finshed, allowing the player to damage enemies and break breakable objects by simply standing next to them. Another useful side-effect of ISG is that link cannot fall off ledges with the glitch activated.
Normal method to perform ISG has been patched in MM3D, but there are 3 different ways to do this glitch, 2 ways involve Deku Link and the other one involves Gibdo BA to 0th day.
For Deku Link's methods: One requires having Sword on B as Deku Link and the other one require Down A as Deku.
Jump slashing into an updraft in Stone Tower Temple makes Deku Link use the deku flowers to fly upward canceling the jump slash animation but keeping the sword's hitbox active.
Note: You need to dupe over deku nuts so the deku flowers don't get rid of your sword
When you hop on the water with Deku Link the B button gets dim (or grey out), by doing Down A while the B button is still grey out you are not restricted to use your items on the bottom screen, being able to do RI with Deku Link. Now that you are able to use the Great Fairy Sword with Deku Link, simply jump slash into the water and land on the ground and you'll have ISG on with the GFS.
By doing Gibdo BA to 0th day you can do a text storage with the carpenter in South Clock Town and interact with the mailbox, then walk to the other mailbox and perform a spin attack without magic (spin attack with magic results on damageless ISG) hold L and press A, thus getting ISG off of the mailbox.