tl;dr: you do things (which seem so far to be able to be done in bot games) and get tokens. While most token rewards are icons or keys, but if you save up a bunch (appears to be about 14 missions worth), you can get things with a Legacy skin shard and a chance of tokens/gemstones/a hextech skin.
You have to decide between two options that have slightly different rewards. I probably should have gone with the Chaos one on my smurf to be able to see both, but eh.
Individual missions are one-day only and I'm not sure how many can be gotten (there are at least two), but it looks like they're expecting an average of seven missions over the two weeks of the event.
The Orb of Order is event-exclusive and contains a guaranteed Legacy skin shard and a 50% chance to get a bonus drop. If your orb triggers a bonus drop, you’ll have a chance to get either a random amount of Order Tokens, two gemstones, or the Hextech-exclusive Hextech Annie skin shard.
I was about to say you don't need to spend money, but then I remembered there are the boosts.
Though the missions from the boosts do require you to play games that include Yasuo or Riven.
Playing Yasuo or Riven...
Only if you try for the big gun quests.
I got two quests done in beginner Twisted Treeline on my smurf.
I think even the big gun quests can be done in bot games, right? So, like, if someone really wanted to, me you and Yobou makes 3.5ths of the squad so getting one would be more likely.
But if you spend money, then you have to play some games on the champ and/or play some games with the champ.
I don't see anything that requires it to be PvP for the big gun quests, though I'm not 100% sure.
I'm hoping bot games count for those, too, because then it becomes so much easier.
Reading them again, they're mostly using the term "matchmade games," which is what they said when I got it with beginner Twisted Treeline.
So you presumably could get even the big gun quests done with beginner bot games. You'd just need to own whichever champ you went with.
I will be going with Order, 90% of the reason being that the Riven seems slightly less edgy than the Yasuo, with 10% being the actual practical reason that I don't want to buy Yasuo.
...With the one downside that you'll probably see more Yasuos and Rivens in games if they aren't banned, who want to get a certain number of kills.
It is good that this event can be done in bot games, as I haven't seen a Yasuo go through since the system got in.
Unrelated heart attack of the day: went down to the exercise room and realized I'd left a small bag that I use to carry my water in downstairs for several days. The bag also included such things as my sunglasses, an ereader, and a checkbook. And the bag had been rifled through with the contents scattered all over.
But then I realized the reason it was left rifled through with my chequebook remaining is because it's also the kids' play room, so the scattered contents are probably not done maliciously.
Okay, now my heart rate should be at a point where I am warmed up for exercise.
Maybe I'll do a shorter session.