Child of Sebek - Sebek Warrior (main weapon - teeth, with a certain number of "Sebek Warriors" in the stack (equal to or greater than the number of units they are attacking), they have a 20% chance to bite through)
The "Harbingers of Death" have a similar skill - "Deadly Strike," or something like that; when it triggers, half the stack is eliminated. But this unit is a higher level and cannot be purchased in a castle.
Regarding the spiders' ability to entangle at a distance - I think it's an exploit.
The skills are repetitive; turtles and tritons dodge.