So, this card is part of one of the most disgusting combos in the game right now

Toss one Hafrún into a Ob together with some Stavka and have anything with a rez cost of 3 rezzed

When the runner approaches Stavka, you rez it, trash the 3-cost card and use Ob to bring Hafrún into the same server as Stavka is. At that moment you can trash one card from HQ to have one of their breakers stop working. If they only have one kind of breaker that can break it, then they're in very bad waters.

There's a few ways to survive this combo.

One of them is, of course, having more than one way of breaking a sentry. Maybe you have your killer, but you also have an AI.

Another way is using something like Flip Switch or Laser Pointer

The other big brain way of getting around this is using Simulchip to reinstall your malfunctioning breaker

But yeah, this combo exists in Startup at the time of this writing, and Simulchip/Flip Switch don't