I realise understanding is not great in this forum sometimes but what is timer based? The appearance of the targets? What is the criteria for level progression?
Or, in pseudo code form:
If number of zombies in timerframes less than
amount needed to progress level then train
will ALWAYS appear
No. The train has its own timer that starts rolling at 0 seconds when you start the level. If you take out (I think) 30 zombies before the train timer reaches like 500 or something the level will advance, ie NO GHOST TRAIN. If you diddle daddle around and dont take out x ammount of zombies before then the train comes.
There are lots of different timers for different things. The train timer only starts rolling from 0 when you start level 4.
The zombies themselves have their own timer and depending on where their individual timers are at will determine how close to the screen they appear/ scale.
So yes it IS possible to take out the required number of zombies to avoid encounter with the train.
Is there any indication to the player how many zombies they need to kill in order to avoid the train?
Do you get to see where the train timer is at and how much time you have left before it appears?
Is it hard to shoot the 30 required zombies to avoid the train in that time?
This is a trial and error thing for the player. Is it fair to the player that they have to figure that out? Maybe not, I don't know. but I do give a hint in the manual to hurry up and shoot as many zombies as they can to clear the level quickly.
Each time you kill a zombie a replacement zombie appears in a random X position. His individual timer starts rolling from 0
Its not a rail shooter to MY knowledge of what a rail shooter is. Maybe you consider this a rail shooter I don't know. When I think of what a rail shooter is I think StarFox SNES where all of the enemies DO appear in the same spots. Or maybe even parts of Zero 5 are like that.