doctorhydrogen

Recurring Nightmare is banned in EDH.

For one more mana than Doom Blade, Putrefy doesn't have the non-black restriction on the creature you can kill and it lets you hit an artifact if need be, or for one more you could run Unmake that doesn't have the non-black restriction on the creature you can kill and it exiles. I'd rune either (or both) over Doom Blade.

Glare of Subdual absolutely destroys people.

Remember that Hex only works if you have six targets. You can't cast it otherwise, though in a Ghave deck it's easy to make a token to kill if need be just to hit six. Still, at six mana I think I'd rather just run Plague Wind at nine and kill all other creatures.

Wheel of Sun and Moon isn't expensive at under four dollars, but it's also not budget. However being able to cycle all your creatures from your graveyard into your library to re-fetch with Sisay seems invaluable.

Battle Mastery not Battle Cry. Battle Mastery gives double strike, and can often times win the game in one shot.

As for things to remove, Divine Favor seems weak as does Murder Investigation, and I'd swap Flickering Ward for Floating Shield.

I like Spirit Loop over Lifelink. It's one mana more, but you can recast it if the creature dies.

Archetype of Courage costs the same as Knighthood, is attached to a body, still counts as an enchantment AND it removes first strike from the enemy.

I'd run Mortify over Murder. Same CMC and you can also hit artifacts with it in an emergency.

I'd get a Black Sun's Zenith in probably over Day of Judgement. Being able to guarantee a board wipe even if there's a Tajic, Theros gods, etc in play is invaluable.

Forgot about that one. Yeah, wildly better.

I'd find room for both 'Tooth and Nail' and 'Defense of the Heart'. Resolving either one into Avacyn + Novablast Wurm is instant GG.

Worldslayer might fit nicely here, too.

For one mana more than Reknit you can run Rootborn Defenses which makes all your creatures indestructible and lets you populate on top of it if need be.

Power Artifact on Memnarch makes it significantly cheaper to use his abilities.

Worldslayer would seem to be Avacyn's best buddy.

Nykthos, Shrine to Nyx would be a horse in a deck with that many permanent enchantments.

Flickering Ward. Trust me, not only is it useful as hell but you can use it draw half a dozen cards in a turn if you have some free mana and an enchantress in play.

I'm guessing you don't have an Argothian Enchantress or Enchantress's Presence down because you don't have either. Both would be uber useful if you can pick them up somehow.

Battle Mastery on a commander like Krond wins games.

Winds of Rath is going to often times wipe the board of all creatures that aren't yours.

I'd run Quicksilver Fountain over Spreading Seas. It will hit multiple people, spreading your islandwalk around, the land stays an island even if the fountain is removed unlike if SS is remove, and if left unchecked the Fountain alone can wreck someone's land base. It can be a win-con unto itself, aside from the ability to grant islandwalk.

Both Wash Out and Innundate feel like blue win-cons, too, if planned well, and can have an impact on the game beyond a turn unlike Breaking Wave or Turnabout.

Quicksilver Fountain kills people in my Talrand deck, as does Back to Basics.

A firebreathing needs Braid of Fire.

All those red mana symbols would really take advantage of a Nykthos, Shrine to Nyx.

Stranglehold and Blood Moon are going to cripple some decks and you won't miss a beat.

Extraplanar lens with a imprinted snow mountain doubles your mana and nobody else can take advantage.

Steel Hellkite would wreck face here.

It's never been a problem for me . . . in four or five player games, which is what I usually play. In larger pods like that the amount of creatures dying far outpaced the amount of artifacts I can recur. If you're playing a lot of 1v1's though that may not be the case.

What I always do when contemplating a change is next time I have the card in hand and am about to play it, I look at the board and think "what if I had the other card, how would that change things?". I would bet that the next few games you play when you're about to cast Go for the Throat you look around and realize that more often than not you'd be better off with a Sever. Maybe not, because a lot of that stuff is heavily meta-dependent, but I'd at least take a look. I actually just pulled Nevinyrall's Dist from my Glissa deck this week in favor of Black Sun's Zenith. I set a goal for myself to look around every time I pulled the Disk to see if I'd have been better off with the Sun, and realized that ever time I had the Disk in hand there were indestructible things in play it wouldn't kill that Zenith would. But like I said, what matters at my table may not matter at yours :)

Since you're running only islands, why not run Back to Basics to screw everyone else?

Cover of Darkness is a pretty great way to make most of your team unblockable, same with Dauthi Embrace.

Terminate > Murder.

I'd find a way to work in Steal Enchantment. BUR has no way to deal with enchantments aside from colorless options (Karn, Spine of Ish Sha) or theft.

Second the Avacyn call, if you're playing to win, that is. I'm not a fan of her in fun games, but if your goal is to crush throats beneath boots then Tooth and Nail or Defense of the Heart into Avacyn/Novablast Wurm does the trick. I actually had to pull the Wurm from my Sigarda deck because it was an auto-win if I pulled Tooth or Defense.

If you're playing multi-player mostly then both Mystic Remora and Rhystic Study will draw you more cards than Thirst for Knowledge 90% of the time.

Bant Charm > Unexpectedly Absent. It does the same thing as absent, but buries it as deep as possible just three mana, and also gives you the flexibility to kill an artifact or counter an instant besides.

While that is true it still has a blue/green color identity making it illegal in a mono-blue EDH deck. From the rules:

"Hybrid mana symbols count as both of their component symbols for this purpose, e.g. if a player uses Isamaru, Hound of Konda as a general, he or she can not use Kitchen Finks."

I suggested it because at the moment it's showing as a B/G deck becuase of Cold-Eyed Selkie. If you're in fact going mono-blue you'll have to pull Selkie.

Mishra's Bauble/Urza's Bauble- Especially since you're running both Viridian Longbow and Thornbite Staff (which combo great with both together on Glissa letting you kill every single creature in a turn). I've had a single Bauble draw me 10+ in a game more times than I can count. They're literally the two most potent cards in my Glissa deck, no exaggeration.

I prefer Do or Die to Diabolic Edict, because pretty often you can take out multiple creatures with it.

Go for the Throat- I personally try to avoid "destroy" effects when it's reasonable to do so. However my meta is filled with indestructible stuff like Theros gods, players using Tajic and Sapling of Kolfenor for commanders, etc. Plus destroy effects just let people play the card again from their graveyard, and in EDH a graveyard is often times a second hand. Sever the Bloodline exiles, so it deals with indestructible stuff, it gets the creature out of range of graveyard schenannigans, and it prevents enter-the-graveyard stuff from triggering like a Wurmcoil Engine split or Grave Pact sacrifice trigger. It does cost four mana and is sorcery speed, though, but it has flashback and can be used to also eat a whole pile of tokens with the same name, which is nice. If you need the instant speed, Silence the Believers exiles, too, but again, it costs four. I think it's worth it in my meta, but YMMV.

Naturalize- Same as above, I avoid "destroy" effects here, too. Naturalize won't handle a Theros god, a Darksteel Forge, etc. and it lets the card be replayed. I'd much prefer to use Fade into Antiquity at sorcery speed, or at least tuck the card with Deglamer or Unravel the Aether.