On a Barrier ice.
And if you try to bring Laamb into this, you’re quickly heading into magical christmas land where 3-card combos that cost >20 credits to play never have to worry about silly things like winning the game.
Sifr is not fine to be taken off entirely. Restricted, I think it would compete with Film Critic and Employee Strike.
The main difference between Sifr and Nexus is that Sifr does nothing by itself. You literally gain zero benefit from installing a Sifr until you install an Icebreaker. Nexus does work all by itself. It’s really sub-optimal by itself (at best, Sunny installing it means they pay x+2 credits to bypass, where x is how much the Corp wants you to pay…) but it does do something, at least. Oh, and the influence cost, which is a real thing. Both of them do invalidate one ice per turn. And even better for Nexus, it invalidates an ice, whether or not it gets past it.
The main thing keeping Sifr on the Banned list is that it has no real downsides and is only one influence. Invalidating one ice per turn isn’t enough to get you on the banned list.
I do think Aumakua+Sifr is the most broken thing you can do with it at this time. Mostly because those cards are one influence each and thus can be played literally everywhere.