While Marth is fast on the ground, Inkling is faster in the air so Marth can't space tippers well against Inkling due to her / his fast speed and Marth's lack of projectile forces him to approach Inkling. Inkling can use splat bombs or splatter shot to pressure Marth in neutral. Splat bombs are hard for Marth to deal with and counter can leave him open. Inkling's bair is safe on shield even against dolphin slash and Inkling's fair can catch Marth approaching in the air and since Inkling back throw is powerful Marth dancing blade on shield can leave him vulnerable to being KOed. However Inkling in disadvantage has a hard time against Marth due to Inkling's dair being slow and Inkling's uair is slow so she / he won't be juggling Marth too well either. But overall Inkling's speed, splat bombs, safe bair give her / him the advantage in this Matchup.
Inkling wins this MU.
While Marth is fast on the ground, Inkling is faster in the air so Marth can't space tippers well against Inkling due to her / his fast speed and Marth's lack of projectile forces him to approach Inkling. Inkling can use splat bombs or splatter shot to pressure Marth in neutral. Splat bombs are hard for Marth to deal with and counter can leave him open. Inkling's bair is safe on shield even against dolphin slash and Inkling's fair can catch Marth approaching in the air and since Inkling back throw is powerful Marth dancing blade on shield can leave him vulnerable to being KOed. However Inkling in disadvantage has a hard time against Marth due to Inkling's dair being slow and Inkling's uair is slow so she / he won't be juggling Marth too well either. But overall Inkling's speed, splat bombs, safe bair give her / him the advantage in this Matchup.
My vote Inkling 6 / Marth 4