Was Waluigi supposed to be a darker character at first?

[warelander]

To be honest I think that Waluigi's weird/wacky nature was already present in Mario Tennis to an extend, the cartoony and overly jolly way he prances around in his trophy celepration scene wouldn't be out of place for modern Waluigi and this is what you would get when starting the game without any controllers plugged in:

So Waluigi is flying(?) away with the N64, so that Luigi can't start the game, again, very much like what a modern Waluigi scenario would look like.

I do agree that Mario Tennis 64 played him a lot more straight as a genuenly villainous figure, but the seeds for what Waluigi would eventually become were already there to an extend.

 

[TB100]

While I think Waluigi was always a wacky and comical character from the beginning. I do think he was originally meant to be a villain rather then the anti hero that he generally is today.
Because he is a primary antagionist in DDR Mario Mix kicking off the events of the game's plot, and as the others have explained in the past, he had some pretty dark undertones in some of his apperences. (Most notably the original Mario Tennis and Mario Party 3.) hell it's even subtly implied that he took over the Mushroom Kingdom in one of the minigames from Mario Party-E (An obscure Mario Party game for the E-reader released only in Japan.)

I'll let TV Tropes explain this one. (From his article on the character page.)

He is implied to have done this to the Mushroom Kingdom itself in a Mario Party-e minigame. The game is called "Waluigi's Reign". It consists of Mario, trapped in a grey room with pipes above him and Waluigi in a cabin above. Waluigi starts to rain down coins and giant hammers at Mario. The number of hammers starts to increase and increase as Mario tries to avoid them. If you notice in the background not only is everything foggy and grey, but there is a construction site halfway finished, almost as it was being build recently. So much for Harmless Villain.

Plus there's this image from the creator of Waluigi himself, which shows him in a more sinister tone, then how he's usually portrayed as.

So I can definitely beileve Waluigi was originally designed to be a more sinister and villainous person then he is nowadays.
Maybe not Bowser levels of evil per se, but probably more along the lines of how Wario was portrayed back when he debuted. (Comical and wacky but also sinister.)