a potion that is made combining a fire charge and a awkward potion it gives the same explosion as
a TNT. if drunk you die instantly (fun for walking around in a creeper skin) if made into a splash potion
it will (as said) make an explosion as big as a TNT
No for many reasons
1-Easily spammable and laggy, so overpowered in PvP.
2-Takes less gunpowder than TnT making it overpowered there.
3-Dispensers and redstone clocks much? Imagine 20 of these a second being lobbed at something. Boom. Gone.