A Train is a Necromancer's trick, flying in one line train of Bone Spirits. It is a very simple trick. We hold the Bone Spirit skill in any of the corners of the screen. After five casts of Spirits, we switch to TP and immediately back to Bone Spirit. The cursor does not move.
After 3 packs there will be about 15 Spirits which is about 75 k magic damage. After the PvP penalty, it's potentially 12 k HP. Almost any character that accidentally flew into such Train dies, or at least loses large amounts of health. Even Barb with 8 k HP.
Even more dangerous will be Invisible Train (Invisible Bone Spirit - IBS). It's a train that was cast before your enemy appeared the mini-map. In this case, it becomes invisible.
!THIS IS IMPORTANT!
The only duel where this trick is a must-have is NvB. In NvB Nec without IBS is a sweet target for Barb. Tank Trick and IBS — these are the two tricks that allow a non-block Necro to win this duel and even maintain the "advantage" (about 60/40 ) above Barb. The rest of the duels (except probably ES Sorc, Zon and a Smiter) a skillful and experienced non-block Necromancer can win without making a single TP and IBS.
Lock (Stomp)/Chain/Chainlock, WSG and Tank Trick — Those are your main assistants in any duel. Your gameplay must not be just IBS spam from one corner of the map to another. You will not learn anything and won't reveal the potential of this character.
Let's go on.
IBS'ing Necro can be caught at the end of another Spirit pack cast.
In that case, you can avoid most of the damage from Spirits. At this very moment, Nec is the most vulnerable, cause he has no Spam-support.
Another option would be not to stomp, but to make an accurate TP next to a Necro's train line (green dot). In this case, you will only catch Spirits from the last released pack (4-5), and their damage will be most likely absorbed by your stack.
The most tricky option against the Druid would be to quickly jump to the head of the Train while waiting to be stomped and run forward at the Spirit line doing WSG. After the Druid stomped you, you cast a Spear to destroy his stack. Without the stack, he will catch the rest of the Train and most likely die.
However, I must repeat. Continuous IBS'ing from one corner of the map to another corner is not an effective tactic against Druid. Decent Druid won't stomp you while you are in IBS. He will cast some Nados ahead of your way and then wait till your Train is about to finish. Only then he will start chasing you with C/T and catch you up already unarmed, without any spam-support. So continuous IBS is pointless.
Use it rarely, but effectively. After 20 seconds of full contact WSG quickly fly away, make IBS in his direction. He might be greedy (sloppy) and fall into the trap.
Another good option for Necro is to cast 2-3 stacks of IBS. As soon as an enemy appears on the mini-map, cast 1-2 "false" Spirit to another direction. Make 1-2 short TP's on that line (make him think that is your failed IBS). Trick him into thinking he caught you vulnerable and when he is about to stomp, quickly fly to the previously casted IBS. The enemy will think that he caught you, but actually, it's him who was tricked.
Good Luck and Have Fun!
Wish you good luck in all your endeavors!