KillFrog.Com is down right now, however, here's a link to "Bad Clues!"
(Parody of the children's show "Blue's Clues" [I'll post the original link(s) when it's back up]
Parts 1-4 are there, respectively):
http://pyrothekitty.tripod.com/badclues.html

More Bad Clues:
(awaiting alternate link)

Original Links (working on and off):
"Bad Clues":
http://www.killfrog.com/newpages/bad.html
And "More Bad Clues":
http://www.killfrog.com/00/bad2.html

And you can buy the classic KillFrog.Com's Flash features on DVD (Vol. 1) here:

UNUSUAL dvd. Relates to Killfrog.com. dvd includes - ultimate survivor, outback attack,little susie experiments,bad clues,skip hop flop,evil piggies show,character profiles and more. (US$15.00)

https://www.ebay.com/itm/Kill-Frog-Entertainment-Studio-DVD-Volume-One-Killfrog-com-/302632614208?_ul=BR

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And, of course ....
NewGrounds.Com ... TONS of cool shit on there ...
But, let's start with an old "shoot'em up" favorite; Pico's School!
http://www.newgrounds.com/pico/pico.html
(And/Or: https://www.newgrounds.com/portal/view/310349)

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I'll find more as I remember them/bother to look for them ...
EDIT: Fixed A Miscopied Link - Thrash

I used to like copying/stealing the flash games from sites and playing them offline.

I think all of your links here are hosed, maybe not all, but...
I have a couple similar working links.
https://retro-flash-games.weebly.com/games.html
https://www.retrogames.cc/

Hahaha I don't seem to have any kind of flash player installed on this machine.

Well. it was from 2+ years ago ...
I'd love to find a good online Flash arcade ....

I used to have one on the old site here but it stopped working ...