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We present VLT/MUSE spectroscopy, along with archival Gemini/GMOSspectroscopy, Magellan/Megacam imaging, and Chandra X-ray emission for SPT-CLJ0305-6225, a z=0.58 major merging galaxy cluster with a large BCG-SZ centroidseparation and a highly disturbed X-ray morphology. The galaxy densitydistribution shows two main overdensities with separations of 0.144 and 0.017arcmin to their respective BCGs. We characterize the central regions of the twocolliding structures, namely 0307-6225N and 0307-6225S, finding velocityderived masses of $M_{200,N}=$ 2.44 $\pm$ 1.41 $\times10^{14}$ M$_\odot$ and$M_{200,S}=$ 3.16 $\pm$ 1.88 $\times10^{14}$ M$_\odot$, with a line-of-sightvelocity difference of $|\Delta v| = 342$ km s$^{-1}$. The total dynamicallyderived mass is consistent with the SZ derived mass of 7.63 h$_{70}^{-1}$ $\pm$1.36 $\times10^{14}$ M$_\odot$. We model the merger using the Monte CarloMerger Analysis Code, estimating a merging angle of 36$^{+14}_{-12}$ degreeswith respect to the plane of the sky. Comparing with simulations of a mergingsystem with a mass ratio of 1:3, we find that the best scenario is that of anongoing merger that began 0.96$^{+0.31}_{-0.18}$ Gyr ago. We also characterizethe galaxy population using H$\delta$ and [OII] $\lambda 3727$ \AA \ lines. Wefind that most of the emission-line galaxies belong to 0307-6225S, close to theX-ray peak position, with a third of them corresponding to red-cluster sequencegalaxies, and the rest to blue galaxies with velocities consistent with recentperiods of accretion. Moreover, we suggest that 0307-6225S suffered a previousmerger, evidenced through the two equally bright BCGs at the center with avelocity difference of $\sim$674 km s$^{-1}$.

Clash of Titans: a MUSE dynamical study of the extreme cluster merger SPT-CL J0307-6225