There's Always a Bigger Train

waited 8-9 seconds after the boss pull (mentally count from one to nine), set toy train on the first path (far from the original position of the boss, it will go on this way the first IH train), and then immediately set the train wrecker robot. I got the train went around the robot as soon as he began to dance in triumph.

This achievement is part the Operator Thogar encounter. To earn it you will need the Toy Train Set and the Wind-Up Train Wrecker toys which you can buy in Stormwind, Orgrimmar or Dalaran.
It's important to note that this is a raid-wide achievement, so you only need ONE person to do this and the whole raid group will get credit for it.

You will need to place the Toy Train Set on the train tracks during the encounter and use the Wind-Up Train Wrecker. After it destroys the Train Set he will turn into an Exulting Wind-Up Train Wrecker and dance for 10 seconds. During these 10 seconds the train from the encounter will need to run over the Exulting Wind-Up Train Wrecker.

Beware, it takes about 5 seconds for the Wind-Up Train Wrecker to smash the Toy Train and turn into the Exulting Wind-Up Train Wrecker so you will need to time the placement of the toys carefully.

Upon reading the words of this achievement, my thoughts will go towards Liam Neeson and the quote that made Star Wars Episode I somewhat bearable, "There's always a bigger fish."

Alright, so down to business.

Easy Achievement for Level 120 Battle for Azeroth and beyond...

1) Normal Difficulty

2) Open up your collectibles menu and type in train, you'll see both the Toy Train Set you need to place and the Wind-up Train Wrecker.

3) So, the first track that you walk past is the one you want, this is the track furthest away from Operator Thogar.

4) Pull the Boss. If you have a pet, even better. Make sure your pet does not kill the boss.

5) Place the Toy Train Set on the tracks furthest from the boss.

6) Wait for the torches to start lighting up above the doors where the massive train will rush through.

7) Once the first torch lights up, place the Wind-up Train Wrecker right beside the Toy Train Set you placed earlier.

8) The Wind-up Train Wrecker will destroy your train, and he'll be happy as a bird, but then WHAM the large train will destroy the Wind-up Train Wrecker.

9) ?

10) Profit. Achievement Completed.