Minibosses (First Block Thebel)
In Persona 3 the main dungeon you are given to explore periodically has minibosses scattered throughout the floors. Each of these minibosses has a unique floor to itself which has a teleporter to mark your progress while scaling the tower. Once you inspect one of these Teleporters you can use it to go back to the entrance or back to this floor at any time you'd like. It's highly recommended that each time you reach a new floor with one of these minibosses you return to the entrance to heal up before attempting them.
The minibosses throughout Tartarus are quite easy and if you actually have a strategy/pick your team members with purpose to negate the enemies strengths and exploit their weaknesses all of these bosses will end up being total push overs.
The whole first block of Tartarus, Thebel can be found on this page. Each of the other blocks of Tartarus though have their own pages - you can find the links to them below this paragraph or at the bottom of each page. It's too much information to put all on one page without making it ridiculously long so I decided to break it up.
Floor 5 - Venus Eagle
Drains Fire // Blocks Wind
Weak to Piercing
Floor 10 - Dancing Hand
Resists Fire, Ice, Electricity and Wind
Weak to Striking
Floor 14 - Rampage Drive
Strong against Slashing and Fire
Lightning does deal normal damage to him.