tyre deflation

Deflating won't help, you need traction in mud, that comes back to tread selection.

i have 33'' mud tyres (simmilar to simex extremes) do i need to deflate them?

18psi is probably standard.

i don't usually drop the pressure in 'pure' mud, but have dropped the pressure by 25% or more to climb a muddy rocky hill.
each situation is slightly different.
rock climbers use very low pressures
'rocking' the steering wheel helps (keep the windows closed).

Try it at 25 psi and at 20 psi and see how it goes. I believe your tyres will wrap and around sharp objects better.

Some tyre will even self clean if you deflate due to the tread bending as it comes off the bottom.

In the end tyre deflation is all about the terrainand the type of tyre.
There is no one rule for every situation

How long is a piece of string?

Basically the lower the pressure, the bigger the footprint, the more traction.

Whether you need to lower the pressures is another thing all together.

I run 50psi when I'm on the bitumen, & if I'm doing any sort of length on dirt I'll drop them back to around 35psi, mainly to help with the comfort when driving thru potholes.

If I'm struggling at all, I'll drop them down again perhaps to 20-25psi. This should be fine for just about anything.

Minimum would be 15psi. Less than this & you risk running the tyre off the rim, so only go this low as a last resort & don't drive over 10-15km/h untill you put more air in them.

Cheers
Richard
2001 Prado GXL TD Auto BFG 265/75R16s MT's