Can you use Beorn with the Trap card Ambush?

Ambush has the text "Combat Action: The engaged player discards Ambush to declare an attack against the attached enemy."

I want to say "yes," as the card doesn't target a hero, just sets up a framework effect. But I'm not too sure. By contrast, Quick Strike has you "exhaust a hero" as part of its cost.

Immune cards "ignore the effects of player cards," so probably Beorn would just have to ignore that attack. Thoughts?

I would lean towards the same interpretation as you. Not sure if there are any relevant rulings on the matter.

Pretty sure Beorn would be able to attack.

Yep, it doesn't mention ''hero'', so Beorn is not directly affected. I'd go for it!

I would say Beorn can be a valid attacker.

His imunity against player cards are to cards that direct towards him.

The Ambush card doesn't towards directly to Beorn. It only creates an attacking stage (that can be before defending) and doesn't specify which characters can be used to attack, as opposite to Quick Strike that creates the same attacking stage but specify the character to be the attacker..

I wondered once, for the same reasons, whether you could use Thicket of Spears to block attacks from immune enemies (ToS targets a "player" and says that enemies cannot attack that player). Turns out you can't, even though the enemy is not directly targeted, but I guess it's different from Ambush. Still, the attack set up b Ambush is a "framework effect" that is enabled by a card effect, and Beorn is supposed to ignore player card effects, so it's very easy to see it both ways.

I went ahead and sent in a rules question.

If I've learned anything, it's that rules involving Beorn or "immune to player card effects" can be determined with the same accuracy as a coin flip. All such questions seem to need an official response to get settled, unfortunately.

And the answer:

"Yes, Beorn can be declared as an attacker with Ambush. The ability on Ambush allows you (the player) to make an attack against the attached enemy. Once the attack is initiated, it resolves like a normal attack, which Beorn can participate in.
The type of attack that Beorn could not participate in, would be an attack initiated by Quick Strike. That’s because Quick Strike instructs you to exhaust a character you control in order to declare that character as an attacker. Beorn’s immunity would prevent you from targeting him with that effect.
Cheers,
Caleb"

Now I'm going to have to make a Beorn Ambush deck

Yeah I put together a deck called "Bear Trap."

I have another Beorn related question:

Can Honour Guard and Close Call prevent damage being dealt to Beorn?

Honour Guard text: Response: Exhaust Honour Guard to cancel the first point of damage just dealt to a character.

Close Call text: Response: Cancel X damage just dealt to a hero.

I have another Beorn related question:

Can Honour Guard and Close Call prevent damage being dealt to Beorn?

Honour Guard text: Response: Exhaust Honour Guard to cancel the first point of damage just dealt to a character.

Close Call text: Response: Cancel X damage just dealt to a hero.

I believe it has been ruled that Honour Guard can. Due to this, I think Close Call should be able to as well. Both effects seem to target the damage (like Dori does).

Yep. Cards that target the damage are legal with Beorn.

Yeah, actually this was the impetus for the Bear Trap deck I mentioned. I wanted to have Beorn out and avoid damage, so Honour Guard of course, but so often it's hard to get Honour Guard out on the table as early as you need him. Damrod and his traps are very good at helping you draw cards. In addition to that, Ambush lets you avoid an attack altogether, so even better for Beorn. I add in Tactics Aragorn for the third hero (more attack avoidance is possible, and the -defense on Aragorn is pretty much the only way to make Beorn stronger).