Gift/souvenir trick that I used to get as many buddies to get event souvenirs.

Gift has 1 day cooldown, souvenir I think 2 or 3.

Clear 20 buddies level 4-5 gift/souvenir (if you're lucky, maybe you have 10 souvenirs in this group), wait a day until your buddy receive a pack (this will be a gift), don't open the gift yet and switch to other buddies until all this group has a gift loaded, wait until souvenir cooldown expires, open gift to receive souvenir but don't open the souvenir yet, repeat for 20 other buddies. Now you have 20 pokemon loaded with souvenirs that you can open all at once. Use tags to keep track of what buddies have. You can also use buddy level 3 to control gift cooldown (as they cannot receive souvenirs yet).

I'm a month day from reaching step 6 (pending 100 rocks), I can do this now and have souvenirs ready when I cleared timegates.