Proper use of Trick Room brings out the potential of many, many mons whose main deficiency is speed. The one I'm going to mention is Escavalier- super high attack, surprisingly high defenses, and just one weakness, plus base 20 speed means in Trick Room it almost always goes first. Swords Dance + Megahorn = KO
But seriously guys, Trick Room. It destroys basically anyone who relies on sweep tactics (like, say, high level gym leaders), and even bridges the gaps caused by Speed EV training, which I usually don't bother with. Trick Room is love, Trick Room is life, because speed is an overrated stat there I said it