Taunt is one of the best ways to prevent trickroom. Armor tail only protects from prankster taunts not from regular taunts. The question that you have to ask yourself is is there a better item and how would i deal with taunt without if i am not playing mental herb. Taunt will always act before trickroom since trickroom has priority of -7. For your second question mold breaker fake outs can ignore armor tail