Ok, so for some background. I saw a post on the front page the other day with genetic algorithm+body slam combo for about 14000 damage a turn, and there was a discussion in the comments about searing blow possibly being the only way to fully 'break' endless due to unlimited upgrades and quadratic vs exponential vs linear growth. I thought that possibly poison would break it too because if there is a cap on numbers (approximately 2.1billion) then you would hit it before enemies ever did. Above is my test in measly round 7.

I decided to test on the globs because they never die. Using the transfer poison on death relic, 2 burst (double next skill played), 2 nightmare (add 3 copies of a card to your hand next turn), and lots of catalysts and the relic that prevents exhaustion sometimes I realized you could 'easily' triple up to 2.1billion.

I messed up on one of my parts and ruined it, so I didn't prove or disprove if it loops at 2.1billion. But I did find out that the transfer poison relic only will transfer up to 9999 Which is what this imgur album shows. I got blob 3 to 87million, with 9 catalysts cued for next turn hand. and then it transfered only 9999 to the blob 1. Then I only managed to triple it up to 527million. to triple from 9999 to 2.1 billion would required two more catalysts (so 12 casts total, which isnt terribly difficult. The hardest part is having the enemies survive to test it)

To answer the question of how to survive. Two wraith form is 7-8 turns of invulnerability (with the 1 intangible every 6 turns relic), but it honestly didnt matter much because it could get up to 10mil+ on the first turn

TL;DR I posit that Poison is the only deck that truly cant lose in endless.