As “Supernatural” heads towards its season 10 finale, star Misha Collins tells Variety that there are “enormous sacrifices” ahead as Castiel and Sam (Jared Padalecki) race to save Dean (Jensen Ackles) from the murderous effects of the Mark of Cain.

Below, Collins previews Castiel’s upcoming road trip with Metatron (Curtis Armstrong), his attempt to make amends with the Novak family, and whether Sam and Cas believe they can succeed at curing Dean — along with an update about Collins’ annual scavenger hunt, GISHWHES.

In the April 15 episode, “Book of the Damned,” Castiel and Metatron go on a road trip to find Castiel’s grace. I’m guessing it doesn’t go particularly smoothly?

Metatron’s personality hasn’t been improved much by becoming a human — in fact, maybe it’s exacerbated a little bit. He’s so excited and giddy about experiencing human sensations that he talks and natters even more than before, so it’s basically Metatron waxing philosophic and Cas telling him to shut up, so it’s very sweet. And not surprisingly, Metatron seems to fail to deliver on his promise in the manner that we are led to believe he will, but I think we all knew that going into it. So there will be some benefits reaped from the road trip, but things do not turn out all rosy in the end.

Elsewhere in the episode, Dean, Sam and Charlie (Felicia Day) are still trying to find a way to remove the Mark of Cain from Dean’s arm. At this point, does Castiel actually believe there’s hope for getting rid of the Mark, or is he just going along with Sam’s desperate schemes because no one wants to face the alternative?

We are all buying into the desperate schemes; they all are not giving up at this stage of the game, and are hell-bent on finding a resolution to Dean’s dilemma. And that really becomes a central storyline for the rest of the season, that’s what the finale is building towards — we’re trying to rescue Dean. “Come hell or high water” becomes the team mantra. And characteristically, we make deals with the devil and the ends justify the means and enormous sacrifices are made in our efforts to cure Dean. There’s a moment in the last episode we shot — we’re shooting things out of order so I can’t remember which episode is which, but suffice to say, there’s an episode towards the end of the season when we make a sacrifice that I was thinking, “How are our characters okay with this? This is terrible, what we’re doing. This is disgusting.” [Laughs.] We’re making some serious compromises in order to rescue Dean.

Hitting new lows, that’s a great headline…

Yes. [Laughs.] ‘“Supernatural’s” central characters hit moral lows in this season.’

And Charlie and Castiel finally get to meet in this week’s episode.

Yes… Both characters have looked forward to meeting the other, and it’s a joyful union.

The April 29 episode, “Angel Heart,” sees Castiel trying to fix the Novaks by reuniting Claire (Kathryn Love Newton) with her missing mother, Amelia (Leisha Hailey). How much is the guilt weighing on him from what he inadvertently did to their family?

Heavily. That’s a key storyline for Cas going into the end of the season. It’s these two things for him: Helping rescue Dean, and Claire — those are the two biggest issues for him. We’re gonna see more of Claire moving forward.

How often does Castiel enter into these schemes with the assumption that he’ll probably end up making things worse? He means well, but chaos generally ensues, even when he’s interfering for a good cause.

I think while they all maintain a certain optimism and naivete, all of the characters on the show are growing increasingly jaded and cynical. I think they’re not wearing those rose-colored glasses most of the time, and that goes for Cas too. They’re becoming hip to the fact that s— doesn’t really go well. The end of the season is going to be more of the same in that department; the season cliffhanger is not gonna be just a collective sigh of relief. When the dust settles, everything is gonna be horrible for everybody.

Bobby (Jim Beaver) was left in a fairly precarious position in heaven after assisting Sam and Castiel with breaking Metatron out — will we revisit that issue soon?

I don’t think we will this season, but… obviously, beyond that, I have no idea.

What’s the motivating force for Castiel in the build-up to the finale, retrieving his grace or fixing Dean?

It’s on fixing Dean, that’s the biggest storyline for him. There’s a certain resignation to him at this point about his own well-being. I think for whatever reason, over the years, Cas has seen that every time he’s tried to do something for his own personal gain, something worse ends up happening for everyone else. So in a way, it feels like Cas is willing to give up on himself, but not on others.

You’re about to embark on another installment of GISHWHES (the Greatest International Scavenger Hunt the World Has Ever Seen) — which raises thousands of dollars every year and has already broken several world records over the past four hunts. Where does the money go and what do you hope to accomplish this year?

It’s become quite a cumbersome operation to run, GISHWHES, with things like the winners’ trip — next month I’m taking last year’s winners to Croatia, and we’re going to the “Game of Thrones” set and doing an island-hopping tour and it’s gonna be a really awesome trip, so some of the money goes to things like that, and some of the money goes to art projects — we’re doing something with drones that I think is gonna be awesome — and then whatever’s left goes to Random Acts [the non-profit charitable organization Collins co-founded in 2010]. This year, we’re building a high school campus in rural Nicaragua in a very under-served community, where there’s a lot of students who basically hike through the jungle to school once a week because they cannot get there every day of the week. So we’re gonna be creating a permanent and regular high school for this extended community, and we’ve even got a bus to get them to school. And that’s coming on the heels of the children’s center that we built in Jacmel, Haiti, coming online. It was a long road because it’s not easy to get projects built and approved by the government in Haiti, but we have triumphed and it is fully operational and that building is awesome. It is totally off the grid, it has solar panels and computers and it’s great — totally self-sufficient and completely self-enclosed.

As far as what we hope to accomplish with GISHWHES this year, it’s kind of like “Supernatural” for me — “Supernatural” had the apocalypse, and then it’s hard after that to figure out “what do you do that’s bigger than the apocalypse?” And last year we got NASA to name a mountain on Mars, officially, “GISHWHES.” That’s really hard to top. I did have a moment when I was processing it, “oh my god, NASA scientists now have to call that mountain GISHWHES when they’re giving the Rover its coordinates, like ‘three degrees south-south-east of GISHWHES…’”

The next step has to be naming a whole star or planet, I’d imagine?

I kinda feel like that would be good, getting a star or planet… I’m excited about it, it’s gonna be a fun year and we have a ton of people [signed up already]. William Shatner is back in the fray, he’s recruited my pal Orlando Jones to be on his team. Registration is open right now and the hunt is in August.

“Supernatural” airs Wednesdays at 9 p.m. on The CW.