Green Lantern's strengths are his incredible b1 combo starter - possibly one of the best footsie tools in the game, his Lantern's Might which is a solid anti-air that (through the liberal use of meter) allows him to set-up easy stage transitions or solid 25%+ combos. His weaknesses are his embarrassingly low mobility and the punishment opportunities present in his strings.
Hal's Strings:
12 and 123 are both massively unsafe strings. 12 finishes at -17 on block, and the same window is present when you block 12 before 3 in the second string.
b12 and b13: the core of every Green Lantern player. b1 is a nasty 9 frame start-up low attack with huge range, but it's -12 on block. The problem is most people let both hits come out (the low, overhead for b12 and the low, mid -> full combo with trait for b13) and these strings are safe on block (unless the Lantern doesn't hit confirm and does b13xx4xxLM, in which case Hal is sitting at -27 point blank. b12 is honestly the easiest mix-up in the game to block so hopefully you don't get hit by it, block low and then block high in the large gap of time you have. Every time you see the b1 sneak out, you either counter-hit them with a fast normal or block high. There's no guessing game.
22, 223, and 2231 are Hal's main damaging strings for in combo, but if he uses it just as an opener (instead of his mix-ups) it's -slightly- punishable on the first hit (if you have a jab that is 8 frame or better.) but mostly you'll get hit with 223xxMG (MB). This pushes you back to a relatively neutral distance which is where Green Lantern's excellent footsie tools comes into play. You don't want to be in this range, so you'll need to either zone or mix him up.
His other strings, f2d1/f2d13/b23/b233, are all safe on block but don't leave Lantern at much advantage. Be careful with b23, if the mace doesn't swing twice Hal is at +4 on block and you can't feasibly put pressure on him.
So how do we beat the Lantern knowing this information? Crouch-blocking is godly against GL. If he can't get b1's off, then you're probably going to win. Green Lantern's wake-up game is pretty lacklustre. Stay out of his b1 range, punish with a d3 or something when he whiffs the attack, and start crossing him over and mixing him up. GL needs momentum and sucks on defense.
Alot of this is essentially correct. Il just add a few things. Firstly, B12 and B13 is not a mixup at all. I dont understand why I see so many Lanterns getting away with it. Moreover I dont understand why so many Lanterns use B12 at all, it doesnt lead to anything except a hard knockdown and Lantern has better ways to get that. Block low for the B1 and block high for the follow up, whether its 2 or 3 a high block will block them both so there is no mixup there at all.
The only way to get a mixup is to do B1 and then do B1 again when they block high for the followup. But as was pointed out above B1 by itself is pretty negative on block so its not the kind of thing I would try unless I already knew my opponent was conditioned to block high for B12 and B13
The main things you have to look out for against Green Lantern are:
B12/B13 As I already said B12 is pretty useless for anything other than conditioning GLs opponent to block high after B1.
B13 however is one of the best whiff punishers in the game, right up there with Supermans F23. Its a launcher that can be hit confirmed and gives GL enough time to activate his trait and still cancel into Lanterns might for a full combo. B1 is also a fast advancing low that covers more distance than you think it does because it has a bit of a phantom hitbox(that is the hitbox for B1 actually extends a little past his foot so he can hit you with it even if his foot doesnt visually touch your character, stupid I know lol)
2,2,3. This is Green Lanterns main block string. It comes out only one frame slower than B1 but is easier on the hitconfirms because its 3 hits. All 3 hits are mid and its safe on block at only -1. On block GL can cancel into minigun to gain some distance from his opponent and due to the pushback from minigun its relatively safe to do so. Some fast advancing specials and supers can punish this though as minigun is like -26 on block.
F3 His standing flip kick is a really fast overhead and GL has lots of ways to be in your face after a hard knockdown and forcing you to guess between his F3 overhead and B1 low. This is the core of GLs mixup game and he has some dirty ways of setting it up. The one Im most fond of is after a MB Lanterns might, GL can dash early to go under his opponent and cross up their block, or dash late to stay on the same side. Both options leave GL right in front of his opponent at stupid advantage. In this situation the B1 is the biggest threat because if done correctly it will hit just as Gl's opponent is hitting the ground effectively teching them up instantly(Its essentially an OTG). If done right B1 will stuff wakeup attacks and backdashes so the only real choice the opponent has is to block B1. This of course opens up the F3 overhead. And while you can wakeup and backdash away from F3, the threat from B1 makes it just to risky. So GL can just go ham on the B1 or F3 mixup. You can fuzzy guard B1 or F3(if your REO and have his kind of reactions) but GL can just delay the B1 and get you when you go to block F3 so the mixup is still there.
Air Oa's rocket. It hits overhead. You have to stand block it. I cant tell you how much damage I get off people just because they keep getting peppered by these trying to duck it or crouch block it.
MB Oa's rocket. You have to be careful when blocking OAs rocket when GL has meter because he has alot of time to meter burn it even after its hit or been blocked by an opponent. From anywhere other than full screen GL can hit B13 as they are coming down and get a full combo. So always be on the lookout for the random meterburn when GL is flinging rockets at you.
Lanterns might. Its inevitable, at some point your going for a ride on the Lanterns might express. This move is like Ermacs push and lift combined into one salt inducing move. Its pretty safe from range so expect to be checked with it alot. It is full combo punished up close but even so Lanterns will YOLO lift even if your in their face so you pretty much have to be looking for it all the freaking time. One thing you need to understand about this move is the hitbox. It has amazing horizontal range, much like Ermacs push. Ive seen it hit as far away as 2/3 screen and even Ive said"I cant believe that hit lol" a time or two. But the vertical range is not that great when your in close to GL. Crossup jump attacks will almost always stuff it and even some normal jumpins will stuff it before it comes out.
You have to play patient against a Lanterns might abusing Lantern and just let them dig their own grave and punish it once your close enough.
The best way to put Lantern in situations he doesnt want to be in is to knock him down, preferably in the corner. Lanterns wakeup options are meh and in the corner backdashing wont save him so you can pour on the pressure. Lantern doesnt like being pressured and he sees a shrink once a week whos helping him to better deal with the pressure in his life, but I digress.
Hopefully some of this helps.
