Use both.

Ability Gained:

[Bigmouth Ring Gag] -- You're capable of telepathically talking to anyone within a 100 feet radius or less individualy or openly.
Allows sending a psychic wave that dazes the mind of those affected.
Your mouth is held permanently open and it will always be a wet, warm hole.
Lips slowly swell around the gag and the mouth becomes gradually more sensitive to sexual pleasure, these changes are permanent.

Ability Gained:

Gemstones of Lust and Desire -- Enables the use of an special breath attack that applies any poison effect the user might know.
Allows the use of a poison that makes affected targets uncontrollably horny, uncapable of fighting, thinking or resisting any kind of advances.
Also makes the bearer's fluids gain a weaker aphrodisiac effect that corrupts after long exposure.
The gems are dropped upon ****.

Some time later you finally finish dragging the passed out elves and the items out of the cave, along with a pair of dragon-like heads. Looking around the cave didn't reveal much about what was happening here. You didn't find a single other hero, meaning they escaped through other means, or those two were the only ones captured.

Before you can decide what to do Rhiannon wakes up. She sits on the ground and places a hand on her stomach before turning to her side and vomiting. She's still being affected by the poison, but looks at you with regret on her face while slowly getting up with a hand on her head.

"What happened?"

You and your brother were captured by the wyrms. I killed both inside the cave. You say, speaking for the first time with your feminine voice.

Now standing she says, surprised, while walking to the outfit you separated near her "So you can talk now, huh?"

Yes, thanks to this item You say, pointing to the gag on your mouth. Combined with your featureless face, the gag forcing a hole through your exoskeleton's head to act as a mouth, which now has full lips, it makes an interesting and very sexual view.

"Cool... you saved us, so you can keep the loot. And now you're pink?"

One of the changes caused by your new items, this one specifically by the gems, was your color changing to pink. There are no pink slimes in nature, so you're even more unique now. I thought it would be a nice change.

"I do like it" she says, getting dressed.

Thanks, you answer. What are your levels? you ask her. She finishes putting the shirt on and looks at you, inquisitively. I think there was something wrong with the contract.

"Well, those wyrms WERE too much for us - and for dozens of other people. We are both level 22, what did you think?"

I think the contract was underleveled on purpose. Someone was trying to send people here to fail. And there were too many failures, too. With each failure the quest goes 1lvl up, so it shouldn't be lvl 20x2, unless someone was keeping it low on purpose. It might have been a bait.

"Bait? For what? Why would anyone want to-"

Rhiannon is interrupted by her brother, groaning loudly. She approaches and helps him sit down, right before he turns to the other side and, just like she did, vomits.

"We... we can talk about later. I have to find what this was about..."