How do I get past Wonder Land's bug problems?

I suggest equipping thunder magic before the fight, like Exo Spark, and just using it when it's right next to you. It'll wipe out all the blocks behind it (assuming they're not the metal or purple blocks) and deal a small amount of damage to it. But to hack away at it successfully, just try to stay right on top of it and whack away. There's no real advice other than run and slash.

Actually, it does help to do the air dash. Use it a few time to catch up to it almost instantly.