From Destinypedia, the Destiny wiki
Dredge Exploders are a special variant of Cursed Thrall that appear when running through the Shrieker corridor right before the Deathsinger in the Crota's End Raid or in the The Founts when patrolling the Dreadnaught.
Dredge Exploders behave like any Cursed Thrall would, but are more durable. A Dredge Exploder can be found during the Crota's End Raid when running through the Shrieker corridor right before The Deathsinger part of the Raid. They spawn in more numbers alongside Ecthar, Sword of Oryx along with other Hive troops as soon as the player opens the doors leading to The Founts.
List of appearances