does Old Man Willow attack every combat phase as soon as he enters play automatically since his engagement level is 50 I am assuming so.
Based just on what you've written, it sounds like you think that enemies with an engagement level higher than your threat will engage and attack you, and therefore with a level of 50 he'll attack everyone. That's not correct. In fact, enemies with an engagement level lower than your threat will engage you -- and once they have engaged you, they will only attack you, and not any other players. Card text can make exceptions to those rules (as with Old Man Willow), but the general rule is that if your threat is low, very few enemies can engage you. That's why one approach to the game can be to keep your threat as low as possible, "sneak past" enemies in the staging area (because an enemy with engagement cost of 30 won't engage you when your threat is 20), and use other methods (like Trap cards or direct-damage effects) to deal with enemies in the staging area without ever engaging them.