Spoilers ahead for Godzilla x Kong: The New Empire! Descriptions printed on the Shimo toys which have started to leak online reveal more about the rival Titan and some of its unique abilities and attributes! According to toy leaks, Shimo is a “Legendary Ice Titan” with “unstoppable and world ending powers”. Shimo faces Godzilla and Kong with a devastating Frost Bite Blast - a projectile weapon much like Godzilla’s Atomic Breath but instead of burning its target, the Frost Bite Blast can literally freeze opponents in battle!
This could be the cause for Godzilla’s evolutionary upgrade - in order to combat Shimo and its powers, Godzilla might need to elevate his abilities - which explains why other Godzilla x Kong toys describe Godzilla with the Pink Spines as being evolved.