Using a much heavier rear tyre than in the front For the last 3 years I've been using light (800grams) tyres front and rear.

Since I've been having too many rear tyre pinch flats (tried everything: high PSI, tubeless, heavy duty tubes) I'd like to switch to a real double ply DH tyre for the rear which weights 1200 grams.

Is running a heavier tyre only on the rear suggested?
Or should I switch both front and rear at once? Maybe for bike balance issues while jumping etc?

p.s. I ride mtb all mountain and downhill
There is no need to have equal tires on both wheels, except for aesthetics.

Just make sure that front tire has enough grip so you can remain in control.

As for getting pinch flats - make sure you mount tubes correctly and they are not trapped between tire and rim. Having high pressure should help you avoid pinches. More durable tire will help with punctures, not with pinch flats.

P.S. My own experience is limited to MTB XC marathons.