WBR is an aggressive midrange deck packed with efficient removal (Requiting Hex, Erode) and resilient threats like Bloodghast, so Mossborn Hydra provides a fast-growing trampling body that outraces their clock and punishes removal that only trades for one counter's worth of damage. Surrak, Elusive Hunter can't be countered and draws cards off their removal-heavy suite, giving valuable card advantage in a grindy race. Meltstrider's Resolve is cut since fighting into their better-statted early creatures (Marauding Mako, Hardened Academic) is unfavorable, and Mole Man's small tokens die too easily to their removal and don't keep pace with the clock.