Xjyuk

I would like to draw a line where A is an accumulation point where the points thicken near it and leave a small trace where you can see the shift to the left of the points. Point B instead is an isolated point. My graph is simply made with Mathcha. I was wondering if it is possible to do it all with the command foreach.

The points move to the left leaving a trace similar to a shadow. See the image taken from the site https://static.oilproject.org/content/13434/puntoaccumulazione.png

My MWE is:

documentclass[10pt]article
usepackagetikz
begindocument
tikzsetevery picture/.style=line width=0.75pt %set default line width to 0.75pt 
begintikzpicture[x=0.75pt,y=0.75pt,yscale=-1,xscale=1]
%uncomment if require: path (0,300); %set diagram left start at 0, and has height of 300
%Straight Lines [id:da1544303409748331] 
draw (112.5,169) -- (386,167.01) ;
draw [shift=(388,167), rotate = 539.5799999999999] [color=rgb, 255:red, 0; green, 0; blue, 0 ][line width=0.75] (10.93,-3.29) .. controls (6.95,-1.4) and (3.31,-0.3) .. (0,0) .. controls (3.31,0.3) and (6.95,1.4) .. (10.93,3.29) ;

%Shape: Circle [id:dp02209809682547026] 
draw [fill=rgb, 255:red, 0; green, 0; blue, 0 ,fill opacity=1 ] (112.5,168.25) .. controls (112.5,164.66) and (115.41,161.75) .. (119,161.75) .. controls (122.59,161.75) and (125.5,164.66) .. (125.5,168.25) .. controls (125.5,171.84) and (122.59,174.75) .. (119,174.75) .. controls (115.41,174.75) and (112.5,171.84) .. (112.5,168.25) -- cycle ;
%Shape: Circle [id:dp22167821914480634] 
draw [fill=rgb, 255:red, 0; green, 0; blue, 0 ,fill opacity=1 ] (131.5,168.25) .. controls (131.5,164.66) and (134.41,161.75) .. (138,161.75) .. controls (141.59,161.75) and (144.5,164.66) .. (144.5,168.25) .. controls (144.5,171.84) and (141.59,174.75) .. (138,174.75) .. controls (134.41,174.75) and (131.5,171.84) .. (131.5,168.25) -- cycle ;
%Shape: Circle [id:dp39173891473190436] 
draw [fill=rgb, 255:red, 0; green, 0; blue, 0 ,fill opacity=1 ] (150.5,168.25) .. controls (150.5,164.66) and (153.41,161.75) .. (157,161.75) .. controls (160.59,161.75) and (163.5,164.66) .. (163.5,168.25) .. controls (163.5,171.84) and (160.59,174.75) .. (157,174.75) .. controls (153.41,174.75) and (150.5,171.84) .. (150.5,168.25) -- cycle ;
%Shape: Circle [id:dp6168290177655962] 
draw [fill=rgb, 255:red, 0; green, 0; blue, 0 ,fill opacity=1 ] (237.25,168) .. controls (237.25,164.41) and (240.16,161.5) .. (243.75,161.5) .. controls (247.34,161.5) and (250.25,164.41) .. (250.25,168) .. controls (250.25,171.59) and (247.34,174.5) .. (243.75,174.5) .. controls (240.16,174.5) and (237.25,171.59) .. (237.25,168) -- cycle ;
% Text Node
draw (119,148) node [align=left] A;
% Text Node
draw (244,147) node [align=left] B;
endtikzpicture
enddocument

The output of my MWE is:

Are you asking for an animation?

documentclass[tikz,border=3.14mm]standalone
begindocument
foreach Y in 1,...,25
begintikzpicture
 draw[thick,-stealth] (-1,0) -- (6,0);
 foreach X in 1,...,Y 
 fill[blue,opacity=X/Y] (5/X,0) circle[radius=2pt];
endtikzpicture
enddocument

This animation is created by running pdflatex and then

 convert -density 300 -delay 24 -loop 0 -alpha remove out.pdf ani.gif

on the generated file out.pdf. If it is too fast or slow, increase or decrease 24.

If I understood right you, for a starting point, following code maybe use.

documentclass[margin=3mm]standalone
usepackagetikz
begindocument
begintikzpicture[>=latex]
draw [->] (0,0)--(5,0);
foreach x [count=i] in 0,0.5,1,3
node at (x,0) [draw, circle, fill=black,opacity=0.2*i, minimum size=1pt](i);
node at ([yshift=2mm] 1.90) A;
node at ([yshift=2mm] 4.90) B;
endtikzpicture
enddocument