Get up as
Definition 1 of 1
Pro Tip 1/3Costume Events
The phrase is often used for dressing up for themed events, such as Halloween or costume parties. 
She's going to get up as a witch for Halloween.
Pro Tip 2/3Planned Outfit
Use 'get up as' when the outfit choice is planned, not something thrown together last-minute. 
He's going to get up as a detective with a full costume he ordered.
Pro Tip 3/3Character Emulation
It implies not only dressing up, but also often adopting the behaviors or mannerisms of the chosen character. 
At the play, they'll get up as historical figures and act like them too.