Fat Princess' Mages and Knights are amazing for approaching him since they can cover her, destroy his projectiles and chock pad and will make very easy combo or super setups.
Her neutral square attack can absorb 2 hits from any square attack in the game when you hold in the button to charge it up so if he tries to go for a suplex grab you can just absorb it and then leave him in a crumple state with the attack.
His Axerang is great for stopping his projectiles especially the air version which comes out very fast and if Dan gets hit the axe will probably hit Sackboy on the way back to returning to him which will stun him making an easy combo for you.
Sir Daniels charge attack when he has his sheild out will eat Sackboys attacks up, destroy his pad and most likely just plow through to hit Sackboy himself.
Dragon Potion fire will be good for destroying the trap if it's directly below you and acts as a deterent since Sackboy will try to avoid walking into the fire.
as a maxed sackboy and 39 in 2v2(last i checked). i think your best approach is gonna be at an downward 45 degree angle. your out of the way of projectiles and the grappling hook doesnt track. what youll need to look out for is the shock pad. If we start the shockpad input it will come out right after weve been hit to interrupt your combo. the pad can be hit or blocked to counter it so depending on your character's move set use what you can to hit the pad as it comes out.
most sackboys just run and wont/cant combo, and will most likely crack under pressure. rush down is a must.
since out jelly balls are reduced in ap its okay if you take a few hits now. But if you get frustrated make sure when you approach, that you watch for the shock pad. sackboy has huge ap combos that can start from that pad.
gg and good luck