I've come pretty close on multiple occasions, but never quite there. I believe my record is Diamond 2. (The ranks go Bronze, Silver, Gold, Platinum, Diamond, Mythic, with tiers going from 4 down to 1.)

The complicating factor is that I recently learned about a bit of deceit that Arena does. Apparently, it keeps its own secret ranking of how good you actually are (whereas the public ranks are much more tied to how much you've played recently) and weights it a lot. (This matches my experience of sometimes being on an improbable winning streak with a new deck and then being unable to replicate it with the same deck at similar ranks.) In addition to mildly perverse incentives, this allows an exploit where you immediately concede a ton of games at the very bottom of a rank (it won't de-rank you mid-season) to tank your secret rating, then win a bunch of easy games. https://hareeb.com/2021/05/23/inside-the-mtg-arena-rating-system/

I would feel somewhat unsatisfied doing this exploit, though. Still, knowing about this all diminishes the appeal for me of getting Mythic the "proper" way. Probably I should just stop caring about pointless video game ranks, period, but I do still kinda wanna be Mythic someday. And I have fun playing good Magic.

Anyway, in the past, I've gotten close when I'm excited about a fun deck and dramatically scale up how much I play, which is otherwise not very frequently. I'm not currently in that state, but I probably will be at some point this year.

Previously, I've made markets for particular seasons (and got Mythic viscerally through @galen!)

So resolves YES when I hit Mythic on Magic The Gathering Arena, regardless of how well-deserved, and NO if it doesn't happen by year's end. Resolves N/A if the Mythic rank is abolished, but not if it's renamed and is functionally the same.

Betting policy: I won't bet very much. Probably just if the market feels very mispriced.

General policy for my markets: In the rare event of a conflict between my resolution criteria and the agreed-upon common-sense spirit of the market, I may resolve it according to the market's spirit or N/A, probably after discussion.