Better Without Elves
Those tree-huggers have gotten too smug for their own good. Someone needs to teach them a lesson! Through sheer force of will and quite a few instances of your plans backfiring (sometimes in a literal sense), you have discovered that certain things besides items can travel through the Alfheim Portal. Time to show them what true Minecraftian ingenuity can accomplish!
ALRIGHT, SERIOUSLY NOW, WHAT IS THIS?
Better Without Elves is a Better With Mods/Botania crossover addon that allows you to wage a proxy war against the denizens of Alfheim. For just a small price of a little bit of mana, you can send any configured explosive entity through the portal, provided the fuse is long enough (I hope you're just putting explosive entities into the config json, because if you don't, I'm going to cry). In exchange, you get some mysterious lumps of flesh and the occasional elven treasure.
Prank your friends! Create a TNT farm! Make sure those hippies pay for respecting nature!