The drop rate for Mythic troops from Legendary Tasks is 0.5%, and 9.5% for Legendary Troop.
The drop chance for a troop from Cedric is 33%. Interestingly, you’re more likely to get the legendary Cedric Sparklesack than any other of the Gnome troops. The exact drop rates, I don’t know, because they’ve introduced new ones often enough that whenever a new one comes out, its drop rate is going to be lower in my statistics than all the rest. However, if I had to guess, I would say the drop rate is approximately 30% for Cedric Sparklesack (when a troop drops that is, you still only have a 33% chance to get ANY troop) and ~10% for the other troops (Treasure, Jewel, Soul, Pet, Glory, and Mecha Gnome). However… I don’t know if the new Daemon Gnome can drop in normal vaults or if it’s limited to Epic Vaults. I also don’t know about Heart of Rage, because it’s a Legendary instead of a common, and I highly doubt it has the same drop rate as Cedric.