Mari 4.2 Release notes
Mirror projection brings highly-requested simultaneous, symmetrical painting workflows to Mari, without the need for specialized UV layouts. Artists can paint on one side of a mirror plane while Mari projects the same paint to the other side of the mirror plane, dramatically increasing artist efficiency. Mirror masking prevents secondary projected paint overlapping across the mirror plane. By masking the opposite side of the mirror plane for each projection, the paint meets at the mirror plane with a perfectly reflected edge. The mirror plane can also be locked onto an object or locator, allowing the reflected edge of the mirror projection to be manipulated to the best symmetrical position and orientation.