I guess streak idea could work, but reward shouldnt be double experience.
But then again how would that streak work? I don't know what your idea of how streak would work, does it only count for one pokemon and resets if you use a different one or do you continue the streak whenever you win a battle? Does it reset when you logout? Or does it reset after you exit the battle?
Each avatar has certain method of unlocking them, adding another option doesn't sound right.
While this could be helpful, I don't think its necessary. Encounter rate is fine as it is.
Skill branches in clans (still not implemented) will be good enough as a reward for being in clan. Seasonal clan rankings would be nice as well.
Pink and ancient pokemon are not in game so lets not go there.
This suggestion I like, first part of it at least. With battling system as it is at the moment, winning consecutive battles wouldn't be hard, you would just spam OP attack on your Dark Pokemon and the competition would just be who can do the most battles in a row without any chance of losing. This could be fixed by making battle tower opponents have stronger and stronger pokemon with each consecutive battle, like raise opponent's pokemon level by 1 after each win (first opponent would have level 100 pokemon) and if you lose you go back to beginning, just like in battle tower in real games. Pokemon with levels over 100 are the only real challange battling wise in game. This would show who can make the best team. Also, just like in battle tower, you'd need to lock in pokemon you are going to use for this challange so you wouldn't be able to change your team. The major problem with trying to get to the first place in season would be refreshing the page. Whenever you refresh the page that battle starts from the beginning and you do not recieve lose. This would get abused a lot and wouldn't be fun. If that can be somehow changed, this could work flawlessly. Rewards could be just like seasonal ones. Best 5 people get unique version of pokemon, 95 others get normal version.
People asked for old events to be back, they got back in forms of mystery boxes, people complain. Having event each day (there are a lot of event pokemon released and still not released) would just ruin the hype for events. Mystery boxes are great idea to bring no longer obtainable pokemon back.
Better filter for this would by type filter. For example, rock, click on rock filter and you get all rock pokemon you have.
Sidequests are untentionally made long, therefor the prizes for longer sidequest regions are harder to get. How would you lower the rarity of them?
Arceus forms already had events for them (water, dark...). There will be Arceus events in future as well. Also, legendary pokemon cannot breed nor can they be in egg so that doesnt make sense.