Is Ranger of the North a player card, an encounter card, or both? If it's not a player card, does that mean its ability works on cards that are "immune to player card effects"?

According to The Lost Realms insert, p 2 (emphasis mine): "Encounter is a new keyword that appears on player cards with an encounter card back ".

Based on that, I'd say they are a player card.

The better design of an ally, which comes out of the encounter deck. The Ranger of Ithilien got an Ally trait

Correct JanB... but that is a card limited to a single scenario unlike Ranger of the North that may have been designed to be used in several scenarios aggregate with Ranger Summons ...

So they needed to make it look like player cards in front but with back of encounter.

Although they could use that design and not put an encounter set....

The better design of an ally, which comes out of the encounter deck. The Ranger of Ithilien got an Ally trait

And nowhere does traits do anything regarding of who control it and if he can be heal like an ally type...

Ally trait has a dead meaning.

For me it's

Sorry for the necro, but when exactly do you insert these into the encounter deck? "In order to shuffle one of the set aside player cards into the encounter deck, a card effect must instruct the player to do so" (Lost Realm instructions p. 2). Having played through the first three quests I didn't come across any card effect telling me to shuffle in a Ranger. What am I missing?

There’s an event card that does it. A player card. I forget it’s name but obviously comes in the same pack

"Ranger Summons" is the name of the event card; it's a one-cost Leadership event.