OK, so I completed Grudge Match - it took me quite a bit to figure out, but overall I didn't have a lot of trouble once I figured out what I was doing (in fact, I think I played rather suboptimally).
I was thinking it might be a good idea to curb EM's RNG element (the way desecrating JJ always punishes you in this puzzle) since if you get unlucky you might get blocked off by a Murkshade or Barbing Bush, forcing you to lose mana to proceed and possibly costing you the puzzle. The EM puzzles in the base game solved this by making every plant a Poisonous Pod - thoughts on this?
I'll post my solution in a spoiler below:
Side note, but what do you mean by "upgrading the Explorer's Guild"? I don't see an option to do that. I've seen videos of the mod with extra preps from the Bazaar and I can't see an option to upgrade those either. Do I need to do a quest or something in order to unlock those? I haven't tried anything on the main map, I've been having too much fun with the puzzles and class challenges!