These tarpits are made up of very cheap models allowing them to field extremely large units. So they go into the fight with many more ranks than their opposition and even after your unit butchers a bunch of them, they still have enough ranks leftover to comfortably claim steadfast. Take your example of the Skavenslaves unit, which I've read usually clock in at 100+ models, they can endure many rounds of losing 10+ models before they ever lose their steadfast. That means they get to take that break test on leadership 10, often with a BSB reroll. Those are good odds. Sure your unit will eventually cut through them, but how long will that take? I think for such a solo character to work, they have to be either Stubborn or Unbreakable. But maybe someone more experienced like @Lord Agragax of Lunaxoatl , @NIGHTBRINGER , @Killer Angel , @Krox_v.2 can weigh in on the topic? What kinds of characters (if any) can take on @Quinn 's deathstar unit that he describes a few posts back? Can they actually constitute a viable counter to such a unit?