Gimli does different types of smash attacks: a normal, anti-enemy attack, a longer, wall-plate breaking attack, a jump floor-smash attack, and a thrown, unnaturally destructive smash attack. To do the normal attack, just press the attack button. Same thing with the wall-plate one, but you need to be next to a cracked plate in the wall. To do the jump floor-smash attack, press jump and then press attack while still in midair. Gimli should do a midair flip (
)and then smash his axe into the floor. For the thrown attack, change to a tall character and pick up Gimli. Aim like with Legolas' bow or some sort of rock and hit the cracked plate. Does that solve the problem?