Just use substrate in his litter box, no need for it all over the cage What type of shavings do you use? I *think* aspen shavings are okay but I believe all others can cause respiratory issues. Something like carefresh would be a good alternative, or even plain wood pellets. I use wood pelleted cat litter (non clumping) and find it very inexpensive and absorbs odours really well!

In regards to the mat, just make sure he doesn’t eat it. Chewing is fine but if he’s swallowing bits, you should remove it. Fleece is usually a safer alternative – still not great if he chews it but a little here and there wouldn’t be too bad. You might already know all that so apologies if I’m boring you lol.

Onto the actual question at hand! I would recommend a hidey box in the pen. A cardboard box would work wonders but if you got a slightly sturdier one, it could also double up as a look out post (just make sure he doesn’t use it to leap out of the pen!) Depending on your bun’s particular preference, you could go for rabbit specific toys or baby toys or diy toys. My rabbits really like knocking down stacking cups and bowling pins. They also like anything willow so willow balls, dumbells, baskets full of hay etc all go down a treat! You could also make some toys out of cardboard. Check out stormyrabbits on YouTube. She has a couple videos for diy toys that are pretty great. She even made a hay ‘carrot’ with timothy hay and sisal twine.

Does Flea like tunnels? Mine like wooden log tunnels, but I can’t trust them with plastic tunnels or fabric-y ones without supervision because my boy chews them lol so wooden ones are good for mine!

Chews! Rabbits love chewing so anything wooden or cardboard you use could double up as a chew toy. I’ve read that many buns chew on furniture rather than rabbity things because furniture is more stable and they can get a good gnaw on it w/o it moving too much. So you could try putting solid attached to the bars of the pen.

http://www.petsathome.com/webapp/wcs/stores/servlet/en/pets/wooden-playsticks-large

^ ^ That can be flattened and cable tied onto bars or can be bent into a tunnel. If you’re in the UK, those are buy one get one half price

I think I’ve covered everything! How big will the pen be? I would keep the hidey home and a tunnel or two at all times and then rotate the toys. It’ll stop him from getting bored and also still leave enough space for him to run around without running into toys hehe.