Thank you!! And yup, I have two save files =)
Honestly, hard mode is not that bad up to the lava layer. It's challenging, but the accessories make it interesting. The lava layer is difficult not because of the lack of light, but because of the stamina nerf (no flask/no boots). The minimum optimum stamina cost of the obsidian layer is ~65 (switch out winterheart & switch to gold pick for max strength), which is nearly the entire health of Grampshell. Even with perfect stamina restore right before the obsidian layer, it can only be done with the optimal strategy, but perfect or near perfect stamina restore is nearly impossible (1 in 100 trillion). Using the titanium pick and getting one free dig on obsidian reduces the cost to ~45 and ups the odds, and getting two free digs further ups the odds (two free digs in a row is more likely than lucky restore cell placement), but even then it's a moonshot because you have to get really lucky with RNG
With Griddle, it's a strategy of using winterheart & omnishard to get as high stamina as possible somewhere in the middle of the lava, and then digging straight down to water. The 150 base stamina vs 75–90 is a night and day difference =)