Yeah blocking low is the fundamental thing to be doing. Doing delayed wakeups can also help with some of the Cross-Up setups he has.
Both b12 and b13 are gapped, which opens up for several opportunities - where backdashing might arguably be the easiest one of your character has a good one with long reach. The gap in B12 is muuuuch bigger than B13. I think you can actually interrupt with a quick poke or a meterburn b3/f3 if you make the right read.
Also, it's hard to interrupt the things he can do after doing power ring on block after b13 - however he is punishable on every option unless he meterburns the Willpower Wall. This particular meta might change with the new Overcharged Lantern buff, where the enhanced version make GL plus on block. Keep in mind though, that he can also cancel the power ring activation into a meterburn f3 (for a high damage overhead option, that armors through your interruption attempts). It does require him to spend 2 bars, so just keep an eye on the meter.
Some GL players like to do some staggering with b1 - however it is -14 on block so it's actually punishable if you read him doing a stagger of the string.
