Magma Worm

Behavior:
The Magma Worm has a single attack in which the worm emerges from the ground, turns around and submerges. The worm leaves a small patch of flame whenever it emerges or submerges, this indicates where it will emerge from. When fighting the worm, it is difficult to fight with other enemies around, as you may be forced to dodge into them. Climbing onto a rope or vine can prevent all damage this worm deals, as it only deals damage through contact when it goes up or down. This is an advantage for engineer's Thermal harpoons. This boss can be very easy to kill with area of effect abilities or abilities that hit more than one target, such as the Mercenary's and, and the Huntress'  and , because the worm has multiple segments that can be damaged. When on low health, the worm will strike faster and move faster, but will become less accurate.

On death, the worm may drop the Burning Witness item.

Elite Version
This is the only elite version of the Magma Worm. The main difference is that the elite Magma Worm's skin is charged with electrical energy (much like the Tesla Coil on each segment of the worm), making its damage range about twice its normal body width. It is also observed that the Overloading Magma Worm's aim is much more accurate than its normal version. These two features together make it very hard to avoid damage each time it dives without an escape skill, double jumps, or very high move speed. The Overloading Magma Worm, like all other elites, has a significant HP increase.
 * Overloading Magma Worm

Magma Worm

Tactics

 * Sometimes will rapidly change aggro even if the current target is alone and dealing it a lot of damage.  This means no players should be complacent if it is not targeting them.
 * Its arrow telegraph will sometimes lag or not appear at all, causing massive damage to unsuspecting players especially if it just spawned.  This is especially common with the Overloading Magma Worm with its increased damage radius.  Recommend all players stay on the move no matter what or when they hear a worm's roar.
 * With the latest update to targeting, its turn radius allows it to nearly hit any slower-moving character.  However, the Worm always turns its head "down" toward the lower part of its head.  If a player can get behind its body (out of under the slope it creates on rising), its "backwards" turn radius is severely limited by this movement.  Sometimes it can be worth dashing through the body instead of getting hit by a full-on charge.
 * Has a habit of spawning almost immediately on Monsoon difficulty.  This can lead to devastatingly short Glass runs.
 * When in multiplayer, its item drop on death will often not appear at the point of death, but instead near another player's character.  The host seems to be the one it most often ends up near.
 * Rockets and other seeking items are great but will lose targeting on the worm after it goes underground.  These need to be fired very close to it or immediately as it is rising, since its descent is much faster than most seeking projectiles. Similarly, any status effects on it will be removed.