Do you mean tanky in a sense of how many attacks he can survive or just raw dmg assuming he gets hit?
For example I've had a wonderfull time playing pandora with a draw engine and benefitting from her high defensive stats and the cards I put into her cause I knew she was going to be the main target.
On the other hand I've enjoyed letting brewmaster get hit without spending resources on defending him, just keeping him barely alive and then healing him up with a few sips cause of double healing aura from drinking problem.
Also, Hard to kill, prospector powered (risk and reward), disguised, teathered outcast misaki with a librarian and shang backing her up can be both of the former described. Until she meets a hanged or decaying aura... or titania nowdays (god that upgrade is so good)
btw in the case of surviving bursts of dmg there are a few masters that could be considered unkillable (unless they meet something like the viks or glowy lazarus - multiplying dmg)
Collodi, hamelin, kirai...