I'm Too Nice. Deal With It.
Well, I started my normal-type challenge already anyway, even though I'm not officially added to the list. I named my charater Red and my rival Blue (accidentally, later I realised that it should have been Green. :/) Chose Charmander as a starter, caught Pidgey (lv 2) and Rattata (lv 3). The small Pidgey kept fainting all the time, so when I soon encountered level 4 Pidgey, I captured it and threw the smaller on on my computer with Charmander. I trained Pidgey and Rattata a little more and then went to capture a Spearow (lv 4). (the more the merrier! ) I trained all three for a while, and entered the Viridian forest when all of them were on level 8. Went through Viridian forest, returned to defeat my rival, trained at Viridian forest (and encountered at least 5 Pikachus in the process :O).
I thought I could finally try challenging Brock when my Pokemon were all lv 12. Surprisingly, I succeeded on the first try. With Geodude, I used Pidgey to use Sand-Attack as many times as possible so Geodude wouldn't do much damage on me during the slow match. Then I used Gust and changed to Spearow when Pidgey's health was low. Spearow used peck until Geodude fainted. With Onix, I made Rattata use Tail Whip as many times as possible, and then just kept attacking, even if Onix used Bide. Because of that, Rattata fainted, but Pidgey finished the job and Onix was defeated as well.
I continued my journey on Route 3 and defeated all trainers. I started to search for Jigglypuff from the grass, I just couldn't find one. Later, when all my pokemon had leveled up once during the search, Jigglypuff appeared. Since my pokemon were already on level 15 and it was only lv 3, I couldn't attack it but kept throwing Pokeballs until it stayed in. I trained Jigglypuff a little after this.
And that is exactly how I always used to battle Brock, regardless of whether I had a monotype team or not. XD Pidgey's Sand Attack just seemed to be the best way of outsmarting those guys.