I learned how to forge in Halo 3 on MCC out of necessity -- I wanted to play jump maps, but there were none. Remember, when the game came out, Halo 3 was completely fucked (you couldn't even edit gametype goals ie: flag, ball, hill spawns), so there is a reason custom content is severely lacking - and why I hate 343 for that matter. Since the major bugs were fixed (a year later), I made a few jump maps (Ghost: Mastery, Ghost: Kung Fu & Longing) and got good at forging.
Recently, I decided to create an MLG map just to liven up the custom community a bit because getting steam rolled by teams of four in hardcore gets annoying (again, fuck 343). The result is my combination of Lockdown, Onslaught, and Amplified -- the best of ball, flag, and slayer on Foundry. Download it, test the 3 gametypes (fun for 1v1s and FFA as well), and let me know what you think. Spawning is questionable at times, but I blame 343 :}
Download in my fileshare, GT: EvaduR
I did have gameplay to go with this post, but my computer crashed when I was working on it. I lost all my files -- thank god I finished the tage though!