You better have a good target to derez. If you compare this to Eli 1.0, you are paying an extra 2 credits for its rez ability, and that's not a small fee. Sure, you have a better chance to land a brain damage and end a run, but if that's your main reason to play Hákarl, there's a few problem with it:

• 5 credit is a lot at early game.
• Its cost becomes even more prohibitive if you don't have a good derez target.
• At midgame, it becomes less useful once the Runner has a fracter ready.
• Its subroutines can still be broken by Boomerang, Botulus, etc.

So therefore, you are not playing Hákarl for its subroutines; you are playing for its wombo-combo potential. For example, you can derez:

• Nico Campaign to reload 9 extra credits.
• Magnet to host an extra virus card.
• Spin Doctor to draw 4 cards in total.
• Anemone to do another guaranteed 2 net damage.

But the big question is: Is this worth an extra 2 credits over Eli 1.0? So far, there's not a lot of good use of this card, so I'm hoping this will change once the entire Midnight Sun set is released.

This card is a $2 premium over an already mediocre Eli 1.0. The only on-rez effects which might be worth considering at a $2 premium are Regolith Mining License and super-janky Anemone, but nobody is less able to spend $5 and 3 influence on rotten shark meat than an Anemone player.

Even if there were an on-rez effect worth a $2 premium, the timing for when you might want to derez something is very limited and an ice will never be the most reliable way to deliver a derez on demand. If derezzing ever becomes a thing, Divert Power does it a lot better than Hakarl. Divert Power can derez multiple cards, it can give you a powerful ice at a discount, and is much more efficient on $ and influence.

Some unsolicited ideas for game designers:

• The rez cost was too high. This is not only $2 worse than a mediocre Eli, it's $1 worse than a terrible Envelope, AND it's a bioroid!
• Brain damage cards don't need to be this expensive or unreliable. Few, if any, corp decks get meaningful value from inflicting a brain damage. Few, if any, runners take meaningful damage from a brain damage besides like early game Adam and Adam decks almost always have workarounds.
• Brain damage effects, particularly easily breakable subroutines, should be priced closer to net/meat damage.
• $2 Divert Power offers a $3 benefit for each card the corp wants to derez and it's rarely played. A $5 ice can support a much stronger effect than "derez a card to MAYBE inflict a brain damage if they are running with no fracter against a corp with $5 and a card the corp wants to derez." Maybe a one-time Afshar ability where the runner can only break one subroutine? Give the corp a meaningful chance to land the brain damage?