Yacopu possesses three basic forms, which are always available to him and useful in different situations. You can change his current form by holding or and pressing ; the direction you are holding influences in which order the forms are switched through; Fish -> Normal -> Flight for and Flight -> Normal -> Fish for .
When Yacopu changes into his flight form, his ears turn into wings. Rapidly press in this form to make him fly! Be careful, however: You cannot turn around while flying (although you can use the to speed up or slow down Yacopu's flight) and flying into an obstacle causes Yacopu to fall straight down and be stunned until he hits the ground, which can have dire consequences. Yacopu also can neither walk nor attack in his flight form, and being in water causes him to rapidly raise to the surface and immobilises him until his form is changed.
This is the form Yacopu always starts out in. It is his most balanced form, enabling him to walk, jump and kick. He cannot fly in this form, however, and can only walk at half his normal speed in water (in addition to being unable to swim), though being submerged increases his jumping height.
When Yacopu transforms into a fish, he becomes able to swim in water at great speed. Apart from being restricted to water, swimming works similarly to flying, but Yacopu may turn around at any time and colliding with walls does not stun him. He is also able to blow one bubble at a time while submerged when the button is pressed, which rises upwards until touching the surface after being spat out and can harm enemies. Fish Yacopu is defenseless on land and can only move there by flopping around when the button is pressed, however.
By collecting certain power-ups, Yacopu can temporarily assume one of five special forms, which usually replace his kicking ability with a special attack. These forms only last for a short time, however, and Yacopu will be unable to change into a primary form, his movement mechanics being stuck at those of his standard form for most special forms.
A flower sprouts on Yacopu's head in this form. For its duration, he may throw seeds into the direction he is facing; the angle and speed at which they are thrown depend on Yacopu's relative horizontal and vertical movement speed at the time the button is pressed. When a seed collides with an enemy, a flower will temporarily grow on its head, immobilising the foe and enabling you to safely push it around until the flower vanishes.
In this form, Yacopu grows an extendable tail consisting of four spheres. Pressing causes him to use said tail to lash into the direction he is facing, which does as much damage as a kick if he hits an enemy with it, but has a greater range.
Yacopu turns into a ball, causing him to bounce continuously. While his bounces are normally no higher than his jumps in normal form, holding down greatly increases their height. Yacopu cannot attack in this form.
Collecting a power-up while in Ball form makes Yacopu shrink. Apart from its size, this form behaves exactly like the normal form.
Collecting a power-up while in Tail form causes Yacopu to grow to twice his normal height and gives him the power to spit fireballs in a straight line, which take out any opponent in their path in one hit, including bosses.