A Nagagog will start off small and blue, but if it takes enough damage, it makes a noise and grows larger, also turning yellow in the process. Further damage will cause it to turn into an even larger version of itself with a reddish color. While the Nagagog is changing into a larger version of itself, it is immune to damage. The Nagagog cannot go back to previous forms.
A Nagagog's HP is lowered faster by attacks when it is in its larger form. It attacks like a wrestler, jumping on top of the player. It may also do a move similar to Donkey Kong's Hand Slap, but without the shockwave. The larger form the Nagagog is in, the more damage and knockback it deals, but the attack speed is slowed down, making them decidedly unthreatening for such a large enemy.
When captured using a Trophy Stand, it will show all 3 forms, regardless of which is caught.
An enemy that might be considered sumo-wrestler shaped, with a funky, decorative twirl on its head and a cute little mouth. As it takes damage, its body increases in size through three distinct levels. Wow, it's almost like a sumo wrestler climbing the ranks to become Yokozuna! Along with the size increase comes a change in color as well--blue, yellow, and red.