Valuable and difficult to locate massive galaxy clusters undergoing extreme mergers, like the Bullet Cluster, can  provide  constraints  on cosmological models, offer important insights into how galaxy clusters evolve and into how they shape the evolution of the  galaxies within them.  Some of the most massive clusters in the  Universe have  been detected  by the  South Pole  Telescope (SPT) using  the  Sunyaev-Zeldovich  effect.    We are carrying out a project to characterize the SPT cluster sample by combining SPT measurements with the Year 1 data from the Dark Energy Survey, and to select the most extreme merging systems.  I will present a subsample of the most disturbed clusters in the SPT sample, and show the differences in the galaxy population’s optical properties with respect to a relaxed cluster sample.  I will conclude by introducing a new project, the DECam eROSITA Survey, designed to cover the eROSITA-DE footprint in order to complement X—ray observations.  This project will open a window of opportunity which could expand our SPT related work to include thousands of X—ray selected systems, in a wider mass range.