Perhaps this can be a new way to do a monotype or a duotype of Reborn.
The Growlithe you get from the police station can be traded for 1 of 18 different pokemon (egg). The possibilites are Tentacool, Axew, Drilbur, Vulpix, Rhyhorn, Staryu, Togepi, Sneasel, Shroomish, Azurill, Cottonee, Frillish, Pawniard, Vullaby, Larvesta, Phantump and more
This pokemon is set per save i believe so there is no soft-resetting involved.
So when this egg hatches, you have to use the types of that pokemon to clear the game.
When you get the egg, you can go as far as you like, but remember that once it hatches you have to only use those types (even if you get axew and have to use 5 noibats)
Is this a good or a bad idea?