Poison immune creatures when using poison wand/rod
When you are mage with poison wand or rod, it is often very annoying that you cannot kill weak creatures like Poison Spiders and Scorpions with it. Those creatures may just follow you, block your way or even poison you badly. Usually they are not worth of using good runes or wave attacks, unless there are lots of them.
You can either carry melee weapon or weaker wand/rod, which is the easiest way. If you are premium, you can use spells like exori vis to kill those nasty little buggers. Weak runes, like LMM and fireball are also good because those creatures have low health.