Instead of giving monsters negative MR, they should have MR but take increased damage from magic.
The changes to jungling this pre-season are super bad for aoe junglers like Sejuani and Zac. As a small compensation, red and blue buffs are getting negative MR. Instead of just keeping this whole AS on tanks/magic damage champions, why not just let us use Mpen? Give monsters like 10-20 MR with a debuff that puts the damage against them back in line with what it would be with negative MR. From there, it would allow Mpen to be viable. It feels bad having to use AS marks on Sejuani, or having basically no optimal mark for Zac because of his blob minigame.