One neat trick with Ravana is in combination with Haas-Bioroid: Architects of Tomorrow: often, you can opt to (or are forced to) make the subroutines on Ravana non-ETRs, which forces the opponent to pass it if they encounter it on a rez in front of a server. If, for example, your only rezzed bioroid is Ansel 1.0, your opponent must break/click through the Ravana to avoid copying Ansel 1.0's bad subs, and then they still pass it, giving an opportunity to trigger Architects. Early game, rezzing a Ravana and using the Architects trigger to immediately rez an Eli/Bran/Ansel elsewhere can provide pseudo-burst economy. That 4 is the same as a Hedge Fund! Admittedly, it a) has to go towards ICE, b) depends on letting the runner through at least one ICE, and c) prevents any benefit of them face-checking that other ICE -- but those are workable. Most bioroids in startup outside of Tyr aren't especially punishing if the runner has a click or two to spare for bad subs.

Any Haas-Bioroid: Architects of Tomorrow deck in startup is probably running all the bioroids available anyway, but among those, Ravana is the backbone of the deck. Plus, if you aren't clicking through, it's expensive as heck to break. At best, Buzzsaw breaks for a credit and two Leech counters. A Ravana on an otherwise-empty central server shuts down any Leech farming unless the runner has a playset of the things on the field. Great Archives protection, especially, against a Criminal looking for easy targets.

Assuming you've already got a bunch of bioroid ice in your deck, the only downside to this card is that it doesn't do anything on it's own. This is really only a problem early game. You can think of this similarly to positional ice, except it's temporal ice - other ice needs to be rezzed first.

It's 2 stronger than Viktor 1.0 for the same price. If you are one of the few people still using that card, swap them for this now.

At first glance, this has similar numbers to Engram Flush or Slot Machine, which are some of the best code gates ever printed. So why isn't this ice seeing serious play?

1. It needs way too many bioroids to work reliably, but very few bioroids are actually good. After the Fairchild 3.0 ban most tournament HB decks currently use 0-4 bioroid ice, usually Bran 1.0 and Ansel 1.0. Ravana needs like 8-10 other bioroids because it's blank until you've managed to draw and rez one. Problem: you can't get to 8+ other bioroids without overloading on expensive Bran/Ansels and including a few bioroids you wouldn't otherwise want (e.g. Eli 1.0 and Fairchild 2.0). Followup problem: Ravana pretty much demands that you neglect much better non-bioroid ices available. Hagen, Drafter, Gatekeeper, plus any imports, you have much better options than scraping the barrel for 10+ bioroids.
2. Until you have enough money for a $6 Bran/Ansel and a $3 Ravana, the best this card can do is pretend to be an additional copy of Eli 1.0. Problem: the ideal number of Elis in a deck is usually 0-1 and never higher than 3.
   
3. Ravana takes setup time. It'll almost never be rezzable turns 1-2, except out of possibly Architects of Tomorrow. Unfortunately, a lot of the bioroids you're running to make this card happy are themselves expensive and hard to rez early. Bioroids don't do much damage to unprepared runners because they can be clicked through. This isn't like an Anansi situation where bankrupting yourself to devastate the runner might be worth it. Bankrupting yourself to remove 2-3 runner clicks is probably not worth it.
4. Ravana is unusually bad in challenging circumstances (e.g. you're having trouble drawing your ice, recovering from Apocalypse, under serious Stargate pressure, or have had multiple ice destroyed or derezzed).
5. Ravana and its friends can be clicked through on face-check. Burning 2 runner clicks is good value against a routine run, but probably not enough value to scare off Stargate/Diversion of Funds/etc.