The Armored Mammoth, as its name suggests, is a Raider Mammoth with armor plating, a ton of HP under that armor, and ridden by a Raider Champion. The Armored Mammoth is significantly bigger than a normal Raider Mammoth, donning red armor and equipped with dragon-like cannons. These monstrosities make their first appearance during the Raiders vs. Bottle Rockets special event, and still accompany Raider invading forces after the conclusion of that event.
The Mammoth Tank is the current top-tier version of the Armored Mammoth as of the 2.9 Patch. It has more health and armor, and better damage resistance. While it lacks the cannon attack of its weaker cousins, the shotgun attack hits extremely hard, enabling it to quickly strip armor or finish off almost any unit that has no armor remaining.
In a mission where Elder Taos is facing Warlord Gantas, the player gets to have weakened versions of 200 hp and 50 armor. However, it seems like a mistake in positioning, as there is no back view of the unit, making the player version firing at the unit behind it though damage is taken somewhere else.
The Armored Mammoth has two attacks. The first one is a shotgun attack from the Champion rider. This attack does 56-84 (x3) damage, so using heavily armored units should work. Units like the Super Tank, and Medium Tank can destroy this unit in about 4-5 good shots. The hit points from the Champion will slowly wear down armor on most armored units.
The other attack is the firing of the cannon attached to the Mammoth's side. This attack has some armor piercing properties, but the real damage comes from its moderately high damage and quality. Most armored units have no damage reduction from this type, so this cannonball will deplete armor. Something that is recommended while fighting against the Mammoth is using a unit with armor at about 300-500+ hit points. Using units with high offense is also recommended! The cannonball shot from the Mammoth does only minor hits. Fortunately, this unit has low offense which allows higher ranked tanks to often deflect the cannon attacks, and the shotgun attack has a 1 in a 5 chance to have it's damage reflected as well.
The real threat is the combination of both these attacks, and the lack of a global attack cooldown! This means the Armored Mammoth can attack practically every turn!
A tactic is to leave other Raider units alive, so that they can still take their turn, lessening the chance that the Armored Mammoth will attack. It'll take two turns of Tank Killers to take these Mammoths down, which is harder when given the limited unit slots these battles. Also, if you have a Big Game Hunter, USE IT. They have 100% crit chance on these guys and will dish out some serious pain.
There are missions where the player will encounter a softened-up version of this unit. The combined armor and HP is reduced to around 250, and damage from both the cannon and the mounted champion are greatly lessened.
Video on beating it: https://www.youtube.com/watch?v=yWJRlEZkloc&feature=youtu.be