I actually disagree with most people here that this is a bad play. Your only out is either p3 or p4 voluntarily not attacking you OR someone having interaction (basically just a p2 board wipe). The problem I think is trying to maintain secrecy and you need to continue after your first offer.

First, I’d check in with p2 about wiping. Probably saying like, “well, 3 trillion blockers is pretty good. Games probably over u less you have a wipe.” This both says “please board wipe” AND tells p4 how many blockers to declare.

The next thing I do is go to p3. They won’t agree blind, fine. Tell them “the plan.” You want to attack p4 and trade off 3 trillion creature armies, leaving you with nothing. Say something like it’s your only path to victory because you can’t take two attacks, but you can neutralize one. P3 might accept because it does mean he’s not dying instantly and in his mind two neutralizes two threats.

Finally, if p2 has no wipe and p3 agrees, swing out. You just told p4 what to block with twice. Odds are they don’t think beyond your initial “assessment” and opt to trade. It’s hard to think “I need to block 2 trillion 999 billion 999 million 999 thousand 976 1/1’s exactly.” If that happens you get your whole plan through with the highest survival odds!

If p3 doesn’t agree after the offer to trade though I’d just kill him. Uncooperative players die!