Spoiler-alert: You have to do this now. Basically, Microsoft and Riot just announced that whoever has Game Pass, gets all LoL champions, all Wild Rift champions, all Valorant agents, and more across all of Riot's games. That's an amazing deal, and you can read the details here.
How To Get All LoL Champions For $1
Now, while the whole Game Pass thing is already a great deal on its own, it gets better once you realize that you can get Game Pass for just $1. By extension, you can basically get all League of Legends Champions for free - because... you know, it's just a dollar.
Here's how: Upgrade your Xbox Live membership with the Game Pass trial. The Game Pass trial will cost you a dollar, and the Xbox Live membership you already paid for. EZ. For as long as your Xbox Live membership continues, you will now have Game Pass. After that, you'll have to keep renewing your Xbox Live membership to keep this going, but that'll only cost you about $60.
Of course, this is only available for as long as Microsoft knowingly keeps this Game Pass trial loophole open. Once they catch onto that and make corrections, you'll be paying a lot more for your LoL champs. Currently, we don't know what happens to your League of Legends champions once your Game Pass membership runs out, but we know that Microsoft and Riot are more likely to close this loophole, once the LoL partnership goes into effect, which is why you have to act fast.