For those wondering if you can add subroutines before ETR, from the official FAQ:

"Can the Corp add subroutines to a piece of grail ice in any order (by using other grail ice)?

Yes. The Corp can add subroutines to grail ice before or after any subroutines, including the subroutine printed on the card."

Galahad is commonly the front-man for a Grail Ice Suite. It is cheap to rez at only 2 and most players face-check using a sentry breaker and may not be prepared to get damaged by a barrier.

Galahad can support or be supported by Lancelot for program desctruction and/or Merlin for net damage and a potential flatline. Another less likely possiblity is Excalibur which may or may not be relevant depending on which server you have located your Ice on. Often central servers get run 1st in multi-run turns, either to deactivate Jinteki: Replicating Perfection, build up Datasucker tokens, during a multiple-run Medium dig or sometimes during a Account Siphon/Vamp and then run unrezzed Ice play. Defending a scoring server with Ash 2X3ZB9CY, Caprice Nisei, Red Herrings, a Nisei MK II agenda token or even Marcus Batty becomes much more effective when it is their own run that turn.

Grail Ice will take up a big chunk of influence in whatever deck it's played in. Decks that synergise such as The Foundry: Refining the Process or possibly NEXT Design: Guarding the Net can support grail Ice and The Foundry in particular is very synergistic since it lets you pull additional Grail Ice to your hand.

In general grail Ice is not particularly good because of the following drawbacks:

1. Moderately high rez-to-strength ratio
2. Influence hungry neutral cards (except for Excalibur)
3. Require additonal Ice to sit in the hand until the runner runs on a server containing rezable Grail Ice. The additional cards clog up the hand and compete for slots with Agendas, Operations and even installables that are not quite ready to hit the table.
4. The Corp has limited deckslots for Ice and usually needs to defend several servers including Centrals, the scoring server and possibly Asset economy, Ice that stays in the hand may become a temporary or permanent 'dead draw', especially if the runner is not running the relevant servers.

Potential Combos:

TL;DR to double the number of subroutines. Since they are both 'when' constant abilties you should be able to trigger them in the order of your choice.

Marcus Batty to try and trigger one of the gained subroutines.

Mumbad City Grid to keep adding additional subroutines.