I watched Gustaffson vs. Jones I, Jones-Cormier II, Gustafsson-Cormier and Gustafsson-Teixeira the other week just to answer this question to myself. This is pretty much gonna be a striking match-- there's nothing about their grappling that would suggest they've developed an edge over the other since the first fight, and Jones is a tall wrestler in the first place and he naturally struggles when he doesn't have a height advantage, so the striking is what remains.
It doesn't always take some amazing strategy to be able to overcome somebody. Sometimes just noticing what other people haven't done, asking yourself "Why?" and having the balls to actually try it is what can make a world champion.
This applies to anything, by the way.
Head movement and feetwork
- Jon Jones' striking is built entirely around his reach and his kicks. He usually uses his reach for elbows because his arms are so long (his elbow can land where most guys' long-hook would), and his jab is sturdy and basic. However, long arms have a drawback in they lose the piston-like speed that lets you pump it out and feint with it, and it makes hooks awkward and gangly, which leads to retardedly-basic boxing: slip the jab, close the distance and land something. The guy's arms will take too long to re-set his defense, and kickers don't usually have great head-movement because it's hard to move your head on one leg with your body in momentum.
This gif from current #1-ranked strawweight Haruo Ochi (you can find more strawweights in the OFFICIAL(!!!) rankings in my sig) is a good example of both the slipping and the long-armed-hook principles.
This leaves the kicks, but Gustafsson figured out a solution to that in their first fight. Dance around to make it hard for Jones to set himself for a good kick (being off-balance against someone with the swarming abilities of Gustafsson isn't a good idea), and if he lands that side-kick to the leg, press forward off of it and throw a bunch of combinations. Doing this swelled up Jon's face.
Jones hasn't showed any solutions to these problems since, by the way. He's leveled up his high-kick and can hide them off both of his legs, which is a challenge for Gustafsson's head movement, but everything else he's modified wouldn't suggest immediate solutions to Sasha's style.
Gustafsson's movement since the first fight includes adding the back-run-- you slip a punch, turn your back to your opponent at a weird angle, and run away before re-setting, he did it a lot while dominating Glover-- which is a real danger against someone with a good high-kick, so leveling up the high-kick might be enough to beat Gustafsson...
Uppercut the body
- Daniel Cormier actually had a lot of success in the first fight attacking Jones' legs and body, for obvious reason. It doesn't take a genius to realize that a tall, thin fighters' stomach won't take punches like someone squat and with the core of current #1-Strawweight Haruo Ochi. Legs, too.
Most fighters are either too dumb, stubborn or unskilled (or limited by injuries) to be able to do this, though, which is why Jones never had to worry about it. His long arms make catching kicks easier, nobody wants to be beneath Jones' elbows, and most fighters' kicking-boxing is too shitty to be able to circumvent this.
Gustafsson's punching style also transitions very naturally to using the uppercut for body-work, and it creates a double-threat since Jones doesn't know where the uppercut's gonna land.
When I was re-watching the first fight I said to myself repeatedly, "It's weird he's not attacking the body or throwing any uppercuts. Both of those are wide open and he's just sticking to his hooks. Especially since Jon's gas tank is what's winning him the fourth and fifth rounds, and bodywork is how you destroy a gas tank..."
Since then, he's added a really powerful uppercut to his arsenal, and it's been on full display in recent wins. So he's learned. An uppercut to the body is also likely to land on the solar plexis, and anybody who's taken one of those can tell you how it hurts.
And there's just the chance the uppercut will land and knock Jones out. Here's a brutal knockout from top~20 strawweight Jeremy Miado (against then~20 strawweight Peng Xue Wen) to illustrate that:
Of course, the problems with body-work is you lower your hand to land the punch, and at close range that leaves you open to Jon's elbows, but Gustafsson has a low guard and focuses heavily on head-movement to make it easier to stuff takedowns [put your hands on your head and put them at your waist and ask yourself "which makes me feel safer against a takedown?"], so that might not even be a problem in the first place. If low hands meant a counter-knockout shot, the first fight wouldn't have been so close.
Burst-combos
- Currently 4th-ranked strawweight Mitsuhisa Sunabe's fight with currently-8th-ranked Daichi Kitakata is a great example of burst-combinations. Unfortunately, I don't have a gif of that, but you can watch it on FightPass if you want. Sunabe's up there with Gustafsson as one of the best burst-punchers in the sport today-- they could probably learn a LOT from each other if they could overcome the language barrier.
Bursting with combinations is the key to Gustafsson's whole style, and when a guy's good at it, your defenses once they start the burst are very limited. You either have to land a counter-shot (Jon's never been much a counter-striker), weather the storm or angle out at the perfect moment, and Jon was only able to weather the storm the first time... and the facial results were obvious. Preventing them from getting in that position in the first place is the best way to deal with it, but Gustafsson's feet-movement and balance make that difficult.
Tap the legs
- This is more ancillary and Gustaffson's unlikely to do it since his leg kicks aren't that great, but piling up the leg kicks lightly-- to where landing them feels more like a tap (but not to the other guy) is an Obvious strategy against someone with the chicken legs of Jon Jones. Here's a highlight of Strawweight GOAT Rambaa Somdet to show what I mean specifically:
And with his combination skill, Gustafsson could very feasibly sneak in lots of light kicks over 25 minutes. He's done it in a lot anyways. His low kicks are a little sloppy-- this is MMA after all, everyone's shitty at something (except the strawweights...)-- so it would make it easier for Jones to catch them and keep Gustafsson on his back, which is why I said this is ancillary. Figured I'd throw it out there, though.