Slowbro is a bipedal, pink Pokémon with a tan, striped belly and a tan muzzle. It has large, vacant eyes, curled ears, and two pointed teeth protruding from its upper jaw. On its hands, it has three clawed fingers, and two clawed toes on its feet. There is a Shellder attached to its tail. This Shellder has a gray, spiraled shell with darker gray spots. There are several spikes across the surface of the Shellder, and it holds onto Slowbro with many sharp teeth. If the Shellder is somehow removed, Slowbro will revert to its unevolved form.
Slowbro has lost the capability to feel pain due to the Shellder's poison. However, it apparently becomes inspired when the Shellder bites down on its tail. While it is capable of unleashing powerful psychic attacks, Slowbro is typically rather peaceful and usually prefers not to fight. Because it can no longer fish using its tail, it instead swims to catch its prey and allows the Shellder to feed on its leftover scraps. Slowbro tends to live near ponds, lakes, and seashores.
In Galar, Slowpoke evolves into Slowbro when a Shellder bites its arm rather than its tail. Slowpokes attract a Shellder to them by wearing cuffs made from Galarica spice and the chemical reaction between the Galarica, the Slowpoke's blood and the Shellder's saliva trigger this evolution. The yellow markings on Slowpoke's head and limbs turn purple while the Shellder becomes permanently anchored to its host's arm. Post-evolution, the Shellder still resembles its Kantonian counterpart, the only noticeable difference being a purple-coloured spike on its top.
The Galarian Slowbro is a Poison/Psychic-type Pokémon. It is also faster and more aggressive than the regular Slowbro, often lashing out at its surroundings in a frenzy. By pulling on the Shellder's tongue, Slowbro can fire toxic fluids from the tip of Shellder's shell.
- Water Pulse - A blast of water that deals moderate damage and can possibly leave the opponent confused.
- Slack Off - Slowbro takes a break to restore its health.
- Amnesia - Slowbro empties its mind and forgets its troubles, allowing itself to fight at its full potential.
- Psychic - Slowbro unleashes a burst of psychic energy that inflicts heavy damage.
- Shell Side Arm - The Galarian Slowbro can fire streams of poisonous fluid from the Shellder attached to its arm.
Slowbro can transform into Mega Slowbro using the Mega Stone Slowbronite. It becomes engulfed by the Shellder to the point where only its head, arms and tail are visible. The spiral Shellder now has an opening at its tip, allowing the tail of Slowbro to stick out, which it balances on due to its legs being engulfed. It can move by bouncing, using its tail as a spring. The spikes on the Shellder are now reduced to four on the bottom section of its body, with the dark spots only visible on its middle section. Mega Slowbro's energy has gathered into Shellder, which has increased its hardness. This allows it to act as an armour so hard that nothing can scratch it.