Inferno Iron Checkpoint Crate can create unavoidable patterns if TNT crates are on the path
I fought this henchman in the 130-135 gems group.
It appeared in The Great Gate level.
The pattern that caused this impossible obstacle was all three blocks down and the middle stacked up with 2 or 3 crates. However, this occurred when there were already two TNT crates (one on the left lane and one on the right lane). This combination caused all three lanes to have obstacles of 2 crates or higher and was therefore impossible to pass without taking a hit.