Ok,
So I've tried drawing things out with him.
Giving him nice things to think about before bed every night.
Waking him after 90 mins of being down to try and restart his sleep cycles.
Making sure he's not too hot.
having more of a bed time routine.
having no routine.
Talking about what he's scared of at night.
putting him in a different room.
In a different bed.
laying down with him.
Bringing him in with us.
limiting TV before bedtime.
and I'm sure there are a few more... but I'm struggling to think right now.
I have another thread in this section.... as the night terrors coincided with us being flooded out of our home for 8 days so I thought that might have been the issue.

He's currently having a day sleep now with a dummy (which he hasn't touched a dummy in nearly a year).
He's 3 years and 5 months old.