Efficient killers, acid shells possess a resistance to energy fields and weapons. Their powerful mutant armor provides them with mobile fortresses into which they withdraw whenever they're sufficiently injured. Once inside their armor, shells spin a radius of death, spraying acid on any foes in range.
Acid Shells would spit acid that dealt energy damage. They were highly resistant to Energy Attacks when outside their shell, as seen by their glowing yellow sheen.At half-health, they retreated into their shell for a period of time, emitting a deadly cloud of poison all around itself during that period, poisoning all nearby Heroes. If you happened to get poisoned, you could use Meditron's Syndrome Shift or Tork's Sporegenesis to cure the effect, but caution was advised when using Tork as the Acid Shell had the same genesis type as Tork. At this point, they were extremely vulnerable to Energy attacks, but were immune to physical damage. If left alone long enough, it would exit this state, and became resistant to Energy Attacks again.
Krel was an excellent choice to counter Acid Shells with. He could run circles around the shell, hitting them with Tribolts and Twinblazes. Twinblaze dealt energy vulnerability,which was especially helpful when in Co-op with Tempests. Once the Acid Shell had entered its second phase, players could use Krel's Supernova and any energy based Variant Abilities he had. Should the Acid Shell survive that and return to its mobile phase a few Twinblazes should finish it off.
- Acid Shell's behavior of retreating to its shell is similar to real world tortoises and even resembled them when they retreated into their shell.
- During the Beta, Acid Shells had a slightly different appearance and appeared in earlier levels.
- Acid Shells could be seen in the Enemy Spotlight, featured on Scaldron, also in the Cryos Co-op Walkthrough, various Beta Livestreams, and a few other videos from Maxis.