The mechanic
The War Mammoth carries the heaviest armor in the game, so raw damage barely scratches it in the first half of the fight. It is slow and hits your base extremely hard if it leaks, making it a genuine wall.
At 50 percent health its war-plates shatter. Its armor drops to zero, its speed jumps to 1.75 times its old pace as it enrages, and 5 armored plate crawlers drop off it and skitter for your base. The mammoth is suddenly far easier to damage but also far faster and no longer alone.
From that point you are fighting a sprinting bare mammoth plus five armored crawlers at the same time, so the back half of the fight is a burst-damage scramble rather than the slow grind of the first half.
How teams beat it
Use armor strip and pierce to get through the plates before the shatter, then unload your biggest burst the instant its armor falls to zero, because it will be racing your base. Keep crowd control and area damage ready for the five plate crawlers that spill out at the same moment.
Like every boss, it fights inside the showdown rules: kill it and it respawns about twenty percent stronger on the rival's lane, let it leak and it crosses unescalated. The full showdown rules are in How a match works.
