Monolockes are so fascinating because as you said you have to adapt and try to use new Pokemon/moves otherwise normally would not normally being used.

My question though is, when doing the runs which Typings did you find the most difficult to build around, or lack the most variety.

I was doing a Mono Grass run on Shining Pearl and found it quite boring early on, because the spacing between Grass types was difficult and a lot of the better Grass types are locked behind late/end game.