[RedRum]

The encounters that are rewarded for individual tasks?
Yeah being required to catch them because running from them halts progression is kind of annoying.

The main legendary that each special research series revolves around come with their own endless supply of Pokeballs and don't allow berries.
Or at least that is how Mew was for me and that's the only one I've completed so far.
This is nice but was slightly annoying to not have known before because I'd worked my ass off to preserve ultra balls for it.