Below is one of the sketches from the Onslaught Style Guide, which is a document given to artists that worked on the set for reference. This sketch shows a "refugee" Wizard, meaning one that is not involved in the Pit-Fights. This Wizard is very "human" looking, unlike the Wizards in Legions. The Wizards in this block's later sets have started "liquifiying" as part of the Mirari's influence over the races of Otaria.
Onslaught cards showing such Wizards include Ghosthelm Courier, Aphetto Alchemist, and Reminisce.