Well, they are separate questions:

1. Tangled Woods . It reads: 'Travel: Exhaust a hero to travel here'. Can do it someone player or only the first player?

...similar? question for this card, but maybe the when revealed forces the player who reveals that card (but it was only in Black Riders, isn't?):

In need of rest : When Revealed: Remove a hero from the quest and attach In Need of Rest to that hero.

...who attachs it? First player? Who reveals it? Up to players?

2. Wild Tenacity : it reads --> When Revealed: Remove X time counters from each enemy in play with the time keyword, where X is the number of players.

....if there are 4 players, each Guardian discount 4 tokens? one-by-one? Or it stops when the time counter is down to 0? For example the Bear Guardian would discard 2 allies, if not. What do you think?

Tangled Woods: The players, as a group, must exhaust a total of one hero. This hero can belong to any player.

In Need of Rest: You remove only one hero from the quest, and that hero can belong to any player.

You might be remembering the 'Peril' keyword from the Lord of the Rings saga expansions, and the special staging step rules for that box as well. In Black Riders (and probably in subsequent LotR saga expansions as well), each player takes turns revealing one card from the encounter deck. In 'classic' LotR, the "encounter deck" is considered to be the entity "revealing" the card (this is straight from the core set rulebook), and not the players. When the 'Peril' keyword appears on a card, it means no player can use any actions or responses until the card is resolved, except for the player revealing the card.

Wild Tenacity: I would remove all time counters at once (one enemy at a time). So in a 4 player game, remove all time counters from Boar's Guardian, then resolve his effect and discard one ally. Put 2 more time counters on Boar's Guardian, but do not remove any more. Then, remove time counters from the next enemy, etc.

Ok, fair answers. Thanks a lot. I will play as you say.