Doomtrain is an iconic fight in final fantasy 6 that being said it would be a great addition to the ff14 primal fights
The fight progression would be as followed
you start at the end of the train in the caboose as you fight adds the “caboose phase” would be a wall monster or a ghost blocking the way, after that you are flung out of the train that is where you have to start a time action event to make your character land on a moving cart on the side of the train from there you move up and attack the outside to get inside again to move up for “middle train cart phase” this phase would involve a pincer fight that both sides of the cart are closing in and would need to kill both end of the cart walls to pass, this could be considered the dps check of the fight , add would be present and at certain points members of the group would be flung outside and they have to fight to get back in. once this phase is over, again another active time event to land on the cart but this time add appear to attack the group with every add killed it would boost the speed of the cart forward until it reaches the back part of the train engine there , you would have to fight more adds at the same time break open the door or wall , either by killing those adds or attacking the wall directly.
Once inside you get 2 mini bosses and the train’s heart, you have to “stun” the mini bosses to be able to attack the heart each mini boss has a color which they paint on different dps and tanks, the trick here is they both have to sync up in life or one of them will revive with one quarter of its health back up. When both mini bosses are down everyone is able to attack the heart of the train after that, one last active time event happens to get on the cart outside , then kill more adds to boost the cart forward to the front of the train, have someone either kill a special add that will switch trains to move the cart in front of the train after that the front of the trains transforms and starts to attack the group at this point a timer appears with a decent amount of time counting down , the group would need to kill the last part of the train to win before that count down reaches zero. All the while with the risk of falling off the cart thru-out the whole encounter. The end final fantasy fanfare, weapon 360, gg let go again.
The main objective of this fight is the have the heart pumping and adrenaline flowing, have little time to think about reactions all flowing from train cart to train cart no periods of pause or rest one thing after another.