My lovely ideas for being a nuisance without anyone explicitly noticing it was me:

1. Put an orange or related fruit in some drawer they never open. Especially devilish if you put it into a drawer with clothes. It is sticky, rots fast, leaves stains, smell never ever leaves. I once forgot to remove one from my backpack as a kid and it was lying round inside for some 2 weeks. Permanent stains, permanently sticky and ultra smelly. It is so nasty, so so nasty!

2. Watering plants with soapy water to kill them. Only works if they do have plants (rare nowadays).

3. Tampering with laundry. Leaving a dye, like pink dye, and stealing one of their red clothes to put it into the laundry so that they don't suspect you too fast. Without putting something they could blame the color on would make it blatantly obvious it was a mischief.

4. Sprinkling breadcrumbs-type things all over their bed and clothes so it becomes itchy. I am not sure what to pick, but if they noticed actual breadcrumbs and they do not eat bread in bed then you will be the primary suspect. I would get something so small it is not noticable but itchy and only do it once is small but evenly spread amounts.