They all mean the same thing, but pogchamp is the name of the emote that "Pog" and "Poggers" is based off of. I think pog and poggers should be alised to Pogchamp, otherwise we have 3 tags that basically mean the same thing
"artist:sublt_skydreams":/tags/artist-colon-sublt_skydreams -> "artist:skydreams":/tags/artist-colon-skydreams
sublt_skydreams is her twitter handle, but her artist tag on here and derpi is just skydreams