Since patch 1.30 Scroll of Speed no longer applies to Goblin Sappers. Perhaps it is good balance change, but it is pretty bad change in game design aspect. Game rules don’t anyhow inform the players that the scroll won’t work on Goblin Sappers. Goblin Sappers already cannot be loaded into Goblin Zeppelins or Transports and cannot be invisible. (BTW Seems to me, it was wrong way of nerf, the right way was to reduce damage and/or increase cost and/or reduce availability (shop limit) etc.) Those can be perceived by the players, who are not acquainted to patch notes, as bugs. So maybe it is worth to give Sappers passive ability (just icon with hint), something like: Unsteady Explosives - This unit cannot be loaded into Goblin Zeppelins or Transports, cannot become invisible and is immune to Scroll of Speed effect.
good idea. Having the tooltip would clarify a whole lot