Okay, the next appearance of Doom I saw was in the 90s Spider-Man cartoon, in the penultimate arc Secret Wars before the final arc. By this point I already know he's a Fantastic Four villain, not Spider-Man, but I still see him in a Spider-Man related media because that's my priority ^^
Later on, I found out this was adapted from the Secret Wars crossover comics, but at that time I just think it was the coolest arc where all the heroes and villains that has guest star so far appeared in a battle ground. Everyone except Fantastic Four and Doom. This was their first and only appearance in the cartoon as far as I remember.
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So I was hyped. I already like Doom from previous appearances, and he didn't disappoint. He kicked Red Skull out of his territory, forcing him to join with the other villains, and ended up as the final boss for the arc. Unfortunately, and I was really angry at the time, I missed the last episode where Spider-Man and team was supposed to fight Doom because I misread the airing schedule.
I only found out what happened from a flashback of the next episode that Doom managed to get Ben to his side by curing his condition, and then Spider-Man gave a speech on powers and responsibility, but that's as far as I knew.
Also, that flashback was the first time I saw his face, and he's more handsome than I thought. I was expecting Darth Vader.