TBN is the shortest tank cooldown you use it in order to gain 50 Blackblood which give us a chance to Delirium, Queitus, and Bloodspiller. Basically you pop it at the start so you can Blood Price + Delirium ( or use it on MT so you can Blood Weapon + Delirium). I use it on tankbuster a too in addition to pair up with my other cooldowns.