I faced off against Typhus of the Death Guard recently, and we played an "open play card" battle(not sure what you call it exactly). The twist we drew was the ability to regenerate D3 wounds to one single model per turn. Typhus, with his 2+ armour save or 4(?)+ invulnerable save, followed by a 5+ feel no pain, followed by an additional 6+ feel no pain(warlord trait), and add in a -1 to hit for all attacks made against him(psycker power) was EXTREMELY tough to take on. Add in the ability to get D3 wounds back per turn, and he literally would not die. Then add in the fact that T'au BS is 4+ almost across the board(becoming 5+ against Typhus), and I still had an entire Death Guard army to kill as WELL as Typhus, and you have yourself a guaranteed Death Guard win. Typhus can also deep strike, and has 4+ attacks at Str7 with -2AP. All that, in less than 250 points, from what I recall(short the D3 regeneration, not that he needed it). Every 8th edition battle I play, I'm further reminded of how hard the T'au got hit with the nerf-bat in their Index.
The days of goodly English is went
Ziss old dog still has a few tricks!