Oh! The first one is just any legendary! Just as long as the sum of its base stats is less that 600.
This would be a good guide to check. Just go there and pick out a legendary that you like that doesn't have 600 or greater in the "Total" column. :3
As for the second, you simply have to pick any Pokémon that evolves, and not evolve it to its final stage throughout the game, i.e. NFE (Not Fully Evolved). You can evolve a Pokémon once if it can still evolve after evolution, though! So you're not stuck with weak Pokémon. :D But yeah that's coals for you, simply meant to make the challenge more interesting.