Need Help! Can't be Duke on hard...

Any advice, or a cheese build... whatever? this dude is impossible for me... I've had two runs that got him down to 5% but I still died. Both runs were with guardian, had lucky RNG, and basically consisted of me spamming slide while circle strafing and bubbling when available. Most of the time I fight him I only get him to a bit over half before stun -> dead.

I don't have jet or grapple yet and don't want to lower difficulty. It's the last crystal I need too :(