Hi, I made some Mono-type challenges in various games and it's really cool.
First was a Poison-type in Pokemon Ruby (I made videos from this one and they are on youtube, I'll see if I can find the links). I had iirc :
Crobat : Confuse ray/Bite/Fly/Steel wing
Tentacruel : Surf/Ice beam/Giga drain/Water pulse
Dustox : Toxic/Protect/Psychic/Aerial ace
Weezing : Shadow ball/Return/Thunderbolt/Explosion
Roselia : Magical leaf/Leech seed/Growth/Grasswhistle
Swalot : Amnesia/Toxic/Sludge bomb/Body slam
I needed Explosion on Weezing for some pokes such as Glacia's Walrein because I'm unlucky with this Sheer Cold :(
That was not too hard because of Crobat, Tentacruel, Weezing and Swalot who were very good. Dustox and Roselia weren't very useful but still.
The next one was a mono-Grass on Sapphire. There was in my party :
Sceptile : Screech/Quick attack/Leaf blade/Pursuit
Ludicolo (impossible without him I think) : Surf/Ice beam/giga drain/fake out
Cradily : Confuse ray/Ingrain/Ancientpower/Acid (Cradily sucks in Sapphire)
Breloom : Bulk up/Strength/Mach punch/Sky uppercut
Vileplume : Sleep powder/Poisonpowder/Moonlight/Petal dance
Cacturne : Sand attack/Faint attack/Bullet seed/Leech seed
Flannery was very hard (I remember having only Lombre remaining with 2 HP, I forgot about Flail). There were also difficulties with Drake and Steven but thanks to Ludicolo and Breloom, it was succeeded.
The third one was a mono-Normal on Pearl. I had some trouble having two pokes but when I had them, it was much easier. But I don't remember the movesets.
Bibarel (I remember having a Simple Bibarel with Charge ray)
Staraptor
Girafarig
Ambipom
Snorlax (I thought about Stockpile and Belly drum but with Belly drum I think it would have been too easy if Snorlax had three Stockpiles so it only had Stockpile)
Cynthia's Lucario was very troublesome once it CH Snorlax, I had to PPwast it :(
And the fourth and last one was a mono-Ground run on HeartGold. A good friend of mine wanted to do a mono-Rock run (he just finished a mono-Flying run) and I just received the game so I decided to do one in the same time, without using OU pokes. There was my team at the end (I defeated Red with it) :
Hippopotas (last Poke caught, only because of the sandstorm) : Protect/Stealth rock/Earthquake/Yawn
Quagsire@Water absorb : Waterfall/Earthquake/Ice beam/Toxic
Steelix : Earthquake/Screech/Crunch/Strength
Sandslash : Sword dance/Earthquake/Shadow claw/Slash
Gligar : Sword dance/Earthquake/Quick attack/X-scissor
Nidoking : Flamethrower/Ice beam/Thunderbolt/Toxic (I got used to give it the choice scarf, thanks mummy)
For this one I used the Set mode so it wasn't that easy...and I was most of the time underleveled (I challenged the 2nd Elite 4 at lvl 53-55 and Red just after this, for example). Some Gym Leaders were hard, such as Pryce, Clair, Sabrina, Erika...Marion's Weavile was also troublesome, because of Ice Punch and Low kick.
And I think i'll do another mono-type run, maybe the mono-bug run in Heart Gold but I'm not sure.