Elpalzi creatures haven't been touched mechanically in about 4 years, so nope. However, the Champ/Vet ones are harder to retreat from than others, and the vast majority of the Elpalzi in the 5/5 invasion were Champ/Vet ones. Other things make it hard to retreat, too, like the damage PCs get from the gidii bombs. It's likely a combination of these two that people were noticing.


-Persida