Gigantification (巨大化 Kyodai-ka) is a transformation taken on by demonic beings. This form increases the user's size and power.
Usage and power
Makyan Gigantification is said to "raise the user's dormant power many tens of times". In Dragon Ball Z: Kyôshū! Saiyan, Garlic Jr.'s power level goes from 2,500 to 3,500 upon transforming, thus presumably making the multiplier 1.4x base.
The Three Lords Ginger, Nicky, and Sansho take this form to fight Goku. Each lord has a quote they say to initiate the transformation, Ginger says "Gingerbread!", Nicky says "Tutti Frutti", and Sansho says "Cheese!". Garlic Jr. also takes on his own version of the form, which gives him a more drastic appearance change.
In the Garlic Jr. Saga, Garlic Jr. once again uses the form, and Spice and Vinegar are able to use the form when under the Makyo Star's influence. Piccolo also uses his body altering powers to take on a Gigantification form to combat Garlic Jr.'s gigantified state, with Piccolo noting that his version of Garlic Jr.'s form was perfected to not lose speed.
Fused Zamasu's huge final stage is a Gigantification, in his case it is a further mutation of the Half-Corrupted form assumed by Fused Zamasu. It is his variant of the Super Saiyan Third Grade form. Fused Zamasu, however, utilized this form in his Super Saiyan Rosé form.
As Fused Zamasu became more and more unstable, he eventually transformed into this state as a result of his great anger and hate at losing to Vegito, combined with the forced mutation from his Light of Divine Justice, Fused Zamasu bulks himself up and grows to become huge, pushing his power even further and adapting to his rage and hate.
According to Gowasu, this form is a result of Zamasu's complex emotions made real. From why humans would make mistakes and fight each other, why the gods would forgive mortals, to why gods and mortals are in fact similar.
However, even after taking on this form Vegito possessed the upper-hand over Fused Zamasu, who could not keep up with his speed. Nevertheless, Fused Zamasu became more durable than ever, surviving Vegito's Final Kamehameha and Savage Strike before he defused and despite the damage, Zamasu received continued to fight with Future Trunks. Slowly gaining more damage each battle, Fused Zamasu couldn't kill Goku or Vegeta and ultimately led to his destruction at the hands of Spirit Bomb Super Saiyan Future Trunks.