Double the Monster, Double the Fun? (DnD 3.5 Encounter building question))

[BRC]

So, I'm wokring on an adventure, and I'm going to use an Efreet for the final boss fight.
Now, here's the thing, in terms of difficulty, what actually works best is a pair of Efreeti, it gets the CR at the level I want it, and it helps with the action economy that frequently plagues big boss fights (The party consists of four characters here).
However, for the story, I'd want a single enemy.
So, here's what I'm thinking, I basically combine the two efreeti into a single one. I take an Efreet, double it's hit points, doubles the number of times per day it gets to use it's SLA's, and give it two actions each round instead of one ( I would roll Initiative twice for it).
Now, is this a good idea? Or by flagrantly ignoring the rules like this am I throwing my players into an unwinnable fight against an unstoppable Juggernaut.

[Corronchilejano]

Seems to me that it's actually worse for the monster than anything, since debuffs would hit "both".

I think it's quite balanced, but add a couple of things to it. Off the top of my head, I'd add +2 Nat AC and +4 Strength too, just to counter a bit the inevitable Ray of Enfeeblement.

[Kansaschaser]

You might think about just giving the Efreet a template or two instead. I sware I saw a template out there that gave an extra head. I can't remember where it was, but that would give the Efreet more mental actions. I think there is also a template from the Savage Species book that gives it more arms for more physical actions and/or attacks.

[BRC]

Seems to me that it's actually worse for the monster than anything, since debuffs would hit "both".

I think it's quite balanced, but add a couple of things to it. Off the top of my head, I'd add +2 Nat AC and +4 Strength too, just to counter a bit the inevitable Ray of Enfeeblement.

Yeah, the way I see it is like this,
Debuffs and Single Target spells are more effective against this type of "Double Monster" than against a pair of identical monsters, and it's easier to flank (Though considering Efreeti can fly, and the party contains no rogues, this may no be a big issue).
HOWEVER, action economy is Huge, and while that is kind of why I'm doing this crazy idea, it means that the PC's will be faced with two-actions each round for the entire fight. As opposed to a two-effriti encounter where they could focus on one, drop him, then only have to deal with one action a round.

The question is, do these things balance each other out?

[Corronchilejano]

Yeah, the way I see it is like this,
Debuffs and Single Target spells are more effective against this type of "Double Monster" than against a pair of identical monsters, and it's easier to flank (Though considering Efreeti can fly, and the party contains no rogues, this may no be a big issue).
HOWEVER, action economy is Huge, and while that is kind of why I'm doing this crazy idea, it means that the PC's will be faced with two-actions each round for the entire fight. As opposed to a two-effriti encounter where they could focus on one, drop him, then only have to deal with one action a round.

The question is, do these things balance each other out?

The creature still has the AC and saves from ONE creature. Sure, they have to beat him into submission, but since every effect still has the chance of affecting him for ONE round at least (a monk stunning him for example), those two actions balance each other out.

Try to make him spread his attacks though. Not nice to roll your fighter anew for no reason.

[Another_Poet]

What you want is this (if I may be so bold).

By those rules, pitting the "double" efreeti against a normal sized party would be CR 9.

edit: for the multiplier, choose 1.

[Telonius]

Spoilers for Shackled City, but advice inside...

Spoiler

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The final boss for Shackled City has something similar going on. The basic concept is that the boss is two beings in one body, each with a different appearance, abilities, and attack style. (Both sides are hostile to the players and both have the same agenda and beliefs). He can switch back and forth once per round as a free action. Each half maintains its own hitpoint total, and effects on one don't carry over to the other. The players have to beat both "halves" in order for them to beat the whole. If one "half" dies, he automatically switches back to the other "half."

The benefit of this is that it basically forces the players into a longer fight, where buffs might run out and more spells are used up.

You might want to try something similar with your Efreet. Maybe have an Efreet and an advanced or Noble Djinn bound together into the same being. A million years bound to the Efreet has allowed the Efreet to overpower the will of the Djinn, and now they're both out for the players' blood.