Star Wars: Clone Wars Season 7 Episode 2 - 3 Ups & 3 Downs
1. Down - Echo's Survival
It seems that Echo attended the Darth Maul/Emperor Palpatine school of unexplained survivals.
When we last saw him, he was pretty clearly killed by an explosion. Though his body was nowhere to be seen, his charred helmet fell into view, and he was standing directly in front of an exploding ship. Surviving that would be superhuman.
Not only that, but when were the Separatists able to find his body? He "died" in the middle of a battle. It's not like recovering an injured clone was enough of a priority for the Separatists that they would somehow drag him away mid battle, all while remaining hidden from the Republic.
If Rise of Skywalker has taught us anything, it's that we'll likely never get an explation as to how Echo survived. Though it's nice to see him again, it's annoying that we'll never know.