Poison Claw
Inflicts damage to 3 units. The damage itself is moderate but you have to also include the poison stacks (up to 10) plus the active skill Burrow.
All of those combined make Arachne a pain to deal with and you will have to run multiple supports unless you are a big whale.
Burrow
Damage immunity to 30 instances of damage. If you don’t remove all instances, you will be stunned for 7 seconds (and killed most likely). Immune to status effect and can’t be removed.
This isn’t awful to deal with as long as you have a couple damage dealers that attack fast enough (Lua, Tiamat with her skill, etc.).
Knockback Immunity
A passive you don’t have to worry about at all since we barely have any units in the game that can move bosses.