Hot off the presses for you folks, the Missed Triggers guide has another article! Bullet points: only two cards (Nine Lives and Mazemind Tome) have triggers that upgrade. Those card have fairly straightforward triggers to resolve but since some of them are state triggers, we've written a bit into how to handle those.

Additionally, a few cards made the article for being… Odd, or challenging cards. Pursued Whale, Sanctum of All, and the Phasing keyword all got special shout-outs, so check those out if you're curious how they're handled (or what makes them challenging).

https://blogs.magicjudges.org/rules/2020/07/01/core-2021-missed-triggers-guide/