Of course, a dedicated Etrata deck will usually have even better ways to cheat this downside: phasing or flickering her out of play before the shuffle, attacking with copies of the original or copying the trigger itself, or even destroying the target with some other assassin in response to fizzle the shuffle
But Wizards seems to have thought better of the whole sideboard premise theres no learn keyword in Avatar , and the Lesson type ends up only mattering when other cards specifically care about it, like Gran-Gran
The Chaos Incarnate deck is themed around Rakdos (black/red) cards and uses Kardur, Doomscourge as a commander to wreak chaos all around the battlefield and force your opponents to attack each other
Hopefully one or more of these options gives you a few ideas for your own Jumbo Cactuar deck
There, I Said It
712.5d Phyrexian Dragon Engine and Mishra, Claimed by Gix meld to form Mishra, Lost to Phyrexia