I can tell you from firsthand experience that Havoc Festival can be a nasty card (especially in 2HG!), speeding the game up for better or for worse by halving life totals constantly and completely shutting down lifegain. But wait, you may say! What if I can just set my life total to a new number, so my opponent gets bled dry by the Festival while I stay golden? The problem with your sensible plan is… the rules say it won’t work.

Any time an effect tells you to set your life total to a specific number, you gain or lose life appropriately. For example, if you trigger your Eternity Vessel to try and reset yourself to 17 life with a Havoc Festival on board, you will be sad. When Vessel tries to set your life to 17, it’ll make you gain life until you’re at 17. Since the Dark Carnival says you can’t gain life at all, the trigger will resolve and do absolutely nothing since you cannot gain life. Sad times ahead!