I'll give you a quick crash course. I haven't really touched code in 6 weeks but it's coming back to me.
[Begin action 100]
0,8,30,0,5
;group,index,x,y,ticks
;putting a -1 will do the following
-1,0,0,0,5
;will show nothing for 5 ticks
0,8,35,0,-1
;will show 0,8 at x:35 for -1 ticks (meaning forever).
So generally if you're adding more frames to make things smoother, you would also decrease tick count. You almost had it in your example.
[TitleBG BackgroundEDIT]
Type = anim
Actionno = 100
Start = 0,0
Mask = 1
[Begin action 100]
0,8,0,0,5
0,8,5,0,5
0,8,10,0,5
0,8,15,0,5
0,8,20,0,5
0,8,25,0,5
0,8,30,0,5
0,8,35,0,-1
will become:
[TitleBG BackgroundEDIT]
Type = anim
Actionno = 100
Start = 0,0
Mask = 1
[Begin action 100]
0,8,0,0,5
0,8,3,0,3
0,8,5,0,3
0,8,7,0,3
0,8,10,0,3
0,8,12,0,3
0,8,15,0,3
0,8,17,0,3
0,8,20,0,3
0,8,22,0,3
0,8,25,0,3
(etc etc)
0,8,35,0,-1
Although that's just how I do things, feel free to experiment.