As it stands, Dota Underlords only represents the increase in power of a unit by their size, and their star rating. It seems Valve wasn't entirely happy with this, and instead, they've turned to the Valve Workshop community and used their evolution designs. In this first batch, units such as Abaddon, Clockwerk and Phantom Assassin (amongst a handful of others) receive a graphical overhaul. Not all the changes are majorly "bling", but they're subtle and effective. The fact Valve are utilising community contributions suggests that in the near future, we should expect much more input from creators. Take a 

How about another peek at the next update?

Coming soon, a large number of heroes will have their looks change as they are combined and upgraded.

Let's take a look.

— Dota Underlords (@DotaUnderlords) July 30, 2019

Abaddon pic.twitter.com/xZ8HICNuxx

— Dota Underlords (@DotaUnderlords) July 30, 2019