As Mega Blastoise, it develops two smaller shells over its arms, each with their own water cannon. The two cannons on its back are replaced by a single, central water cannon of greater size that can retract into its shell. This cannon extends forward over Mega Blastoise's head and is said to have a blast range of over 6 miles (10 kilometers).<ref>[https://web.archive.org/web/20150329055725/http://www.pokemonxy.com/en-us/pokemon/mega_pokemon/ Pokémon X and Y site | Mega Pokémon (archived)]</ref> Small ridges develop over its now-red eyes and extend to its ears. The ears angle slightly backward and there is a small point on its chin.
As Gigantamax Blastoise, it becomes larger. The pupils become white with bright blue sclera. The blue arms, heads, and legs change to light blue. The underside of the shell is now colored dark red. The shell transforms into a battleship-like shell with 31 cannons of different sizes.
Some of the twin cannons emerge from hexagon or rectangle-shaped holes within the shell. Several white triangle spots are located on its tail and legs. Three red clouds surround the main cannon.
Gigantamax Blastoise can adapt to any situation using various cannon combinations. It never aims in battle as it prefers to overwhelm its opponent by launching dynamic, powerful torrents from its cannons. According to one legend, its cannon is so staggeringly powerful it can blast holes through the mountains. Gigantamax Blastoise can also move its 12 cannons surrounding the main cannon individually to attack in any direction it aligns<ref>https://swordshield.pokemon.com/en-us/expansionpass/pokemon/gigantamax-blastoise/</ref>.