Gravity is assigned rather than increased by some elements

[LBPHacker]

Namely: GBMB, GPMP, and GRVT, and also tools PGRV and NGRV.

94ea50d fixes the problem but comes with usability issues: GRVT, PGRV, and NGRV naturally stack, so their strengths are now all over the place and have to be recalibrated. This also throws compatibility to the wind; not sure what to do about that.

[Jakav-N]

Compatibility will probably have to be dealt with as another simulation option. Perhaps a few other things should be addressed with that? I'm not sure what though as it should at least be relevant. Another possibility would be to decrease GRVT strength on spawn. PGRV and NGRV could probably be modified not to stack. GBMB could also cause compatibility issues because azure bombs for one would probably break. GPMP would have problems too. The more I think about it I think a simulation option is the best way, like for heat simulation right now.