Question: forest spider is turned over during staging. During encounter phase the spider Engages me. Spider ability says forced: when he engages a player he gets + 1 attack till end of turn. Does forest spider get this buff every round if I don't kill him. I don't know if it means when he initially engages me. Thanks

Just until the end of the round. If he stays engaged with you, then he will only use his printed attack value of 2 on the next turn. If you were to use some card to return him to the staging area, like A Light in the Dark, and then engage the spider a second time, he would get the buff once more.

Gotcha , thanks,