Dabi

Dabi, dubbed as Blueflame by Geten, is a major supporting antagonist in the series, a villain affiliated with the League of Villains, and was a member of the organization's Vanguard Action Squad. His real name is Touya Todoroki one of Endeavor's son and the eldest brother of Shoto Todoroki.

Overview
Jab - slowest in the game

Unblockable - very little extra range, fairly slow but not slowest in the game. It's pretty bad, but it's still useable to throw your enemy off guard occasionally (on the rare occasion that you're on the ground). However, unlike some other unblockables, you can combo from it.

Armour - slow start-up, high damage, will win every single trade (unless the enemy DCs away, which is only possible with very fast armours).

Q1 - fireball, quite slow start up, tracks enemy well after Q1 is pressed again - annoying

Q2 - not as useless as some people say it is. The startup is pretty fast, so it can be used to catch enemy off guard. Also puts a lot of distance in blockstrings. Spamming this is straight up retarded because it's one of the most punishable moves in the game - only useful to spam in extremely laggy matches

Air Q2 - very fast start up, high skill required to use effectively - doesn't have to be perfect but you need the right range, and the right angle. However, it's second best projectile in the game (losing out only to Inasa's tornado), and the main reason he's S tier.

TQ2 - trap. Self explanatory, put one down on your opponent after knocking them down, otherwise they're mostly just minor inconveniences for the enemy. For completeness, if you hate fun you can put two traps on top of you (bonus points for if you do it in the corner)

BNB 1: AA DC A Q2 Jump AA DC AA TA - low damage (86), really good at getting wallsplats.

BNB 2: AAA (1 hit on third A) TQ2 Jump AA Q2 Q1 DC AA Q1 Dash AA TA - moderate damage (91), bad for wallsplats. Also very hard to pull off consistently if there's even a little lag.

Best extensions in my experience are Bakugou and Shig. Whether or not bakugou is worth it is debatable (although it's good for securing wallsplats at longer distances, and allows you to get a TA in before doing so). However, in Shig's case, the cooldown is so fast that there's no real reason not to extend with him, and it's a free 20 damage.

Wall reset - Q1 red. Level 3 means the round is almost won, apart from when the wall level 3 bugs out and does similar damage to a level 1. When timed imperfectly (it's almost impossible to time perfectly consistently), it can be interrupted by extremely fast moves like PU2s, Toga's and Kirishima's PU1, Shig's Q1 and SS Deku's Q2.

Wall bounce - use Q1 to get a small extension.

Ground blockstrings - on the ground AA TQ2 (unblockable if they're still blocking) or AA Q2. AA TQ2 can be interrupted by a jab between the second A and the TQ2; AA Q2 can be interrupted by an armour between the second A and the Q2. Switch between these regularly to keep your opponent guessing.

Air blockstring - A Q2 Dash A Q2 Dash A Q2 Dash A Q2 Dash A Q2. Very difficult to perfect, but it's almost impossible to escape (except with basically frame 1 moves like Toga's PU1, but even then you have to time it perfectly).

When the enemy armours, you can use the same principle that the air blockstring uses to throw a Q2 into their face (sometimes jabbing before doing so is more effective to make sure the Q2 hits), dashing then throwing another Q2. This will knock them out of their armour.

Other than all that, Dabi really just requires practice. 90% of his character skill is perfecting the air Q2.