The randomizer mode randomizes every encounterable pokémon. This includes all wild pokémon and all trainer pokémon. The randomizer basically runs a RNG from 1-649 where every number is a pokedex entry. In 1.4 the gen VI pokemon were added as well, which makes the RNG work from 1-703.
Fakemon and Delta Pokemon are not obtainable/encounterable in the Randomizer mode.
You can combine the Randomizer with other challenges. Recommended challenge combinations are:
- Randomizer + Mystery Run
- Randomizer + Nuzlocke
- Randomizer + Bravery
- Randomizer + Nuzlocke + Solorun (be aware this is quite challenging)