Which 5th level spell for my cleric?

[Wycen]

I just realized my PC's cohort has an extra 5th level spell slot and I'm trying to decide what spell I should put in that slot.

Here are my top 3 contenders and why:

1. Unleash Pandemonium. This 5th level spell from Sword of Valor creates a burst of storm activity that deafens anyone in the area, with no save. They also can make a will save to avoid being shaken.

2. Deathless. This 4th level spell from the mythic rules essentially keeps you from being killed by straight hit point damage, until the duration expires.

3. Spit Venom. This 4th level spell blinds the target for 1 round, no save or SR. Has the possibility of poisoning the target as well.

I like the first option because we expect to be fighting a green dragon and most of our group does not take spell resistance into account (or they do by hoping spell penetration will work). So no save and the dragon's initiative is lowered plus a possibility that it fails any concentration checks for spells it might throw our way.

I like the 2nd option because I don't want to get caught in a claw/claw/bite/wing/wing/tail/whatever else situation and being able to essentially defer all that damage (if it gets through stoneskin) would let me sleep better at night.

The 3rd option in one of those few spells with no SR and save (well, versus the poison, but that's secondary to the blindness). The duration is only 1 round, but that's one round to escape with.

Because I know somebody will ask, our party consists of:
Summoner
Cleric focused on stealth and healing
Sorcerer focused on evocation
Wizard who sometimes pulls brilliant things out of thin air but can't remember what he was told 30 minutes earlier
Druid
And a rogue of some sort who just joined us who we have hand waved into the party.
Plus the cleric cohort.

We expect to encounter a mythic green dragon. I anticipate that while we may try to parley, eventually the wizard or sorcerer will provoke a fight. The sorcerer wants something in the dragon's hoard and the wizard encountered the dragon in a past life.

[Hogeyhead]

Blindness is stronger than deafness, but one round is very short for a 5th level spell. Deaf is strong against casters, dragons included. Go with Unleash pandemonium. No to deathless because you have 2 high level clerics in the team, and a high level druid. If someone's in trouble someone can cast a heal.

[Kayerloth]

Some thoughts and questions in no particular order:

What are his other typically memorized spells?
Blindness can be very beneficial when anyone is using sneak attack. But blindness will not effectively "blind" (at least within 60ft) a dragon since they have Blindsight --> "Blinding attacks do not penalize creatures that use blindsight".
Any idea what if any Mythic powers/abilities the dragon may have?
Does he or anyone else have Fickle Winds --> Fickle Winds vs gaseous BW?
What level is the cohort (9th or higher yet?)?

[Axebeard]

Leave the slot open. Take 15 minutes between encounters and either prepare a spell the party needs at that time (raise dead) or re-prepare a spell he's already cast.

[Wycen]

We don't yet have anyone who can cast Heal, Breath of Life is the best for the moment.

The cleric cohort has a specific spell load for fighting a dragon. The stealth cleric just discovered his spell selection is hampered by a hallway that dispels illusions (invisibility) and flight. The druid probably did a little customization, but I don't know to what degree.

The wizard says he keeps one spell slot open for each level to overcome challenges we run into, but I don't know the truth of that. I suspect it is true because he seems to run out of spells pretty fast in extended combat. That is partly exasperated by the fact I don't think he bothers to craft scrolls. If we find a scroll, it is scribed into his spellbook(s) and as a campaign goal he's collected nearly every spell from levels 0 to 3 or 4, so it isn't that he doesn't have access to spells. The player doesn't bother to spend out of game time worrying about the game. When we first gained a mythic tier I posted to our group the "easy steps to making your character mythic" and 2 weeks later at the game table he asked me how to update his character.

My assumption of the dragon's lethality is based on remembering our previous battle with a non-mythic black dragon.

[Wycen]

Status update.

The dragon, or the DM really really rolled horribly. He failed nearly every save and lost a spell to being deaf thanks to Unleash Pandemonium.

So now we are trying to decide how to split the loot.

[Valkir]

Horizontally?

;)