I was under the impression that the intent is that the block would fill up the pit almost entirely, so the GC gets completely expelled from it. Yeah, the block would weight tons.
If it nearly filled the pit it would be extremely peculiar in effect and might not be able to sink at all if GCs turn out, like water, to be incompressible but vastly more viscous than water.
Also, if it did do that (i.e. nearly fill the pit), there is NO POSSIBLE WAY the Yellow Mold would impact-trigger, because the speed of impact would be low and the deceleration incredibly gentle, as the viscous semi-liquid was slowly sprayed out as a sort of sheet of goo as the block descended. Even then it is extremely unlikely the goo would make it outside 5-10' from the pit.
Also big problem if the block is 10x10x10. No-one can possibly get hit by the Yellow Mold if it triggers.
Yellow Mold in 1E hits 1" cube centered on it. I.e. 10x10x10 in later terms. So only people literally ON TOP of the block could possibly be hit by the Yellow Mold.
This design is completely broken. The Yellow Mold fails in at least FOUR different ways:
1) In many scenarios it catches fire.
2) In all non-added-to scenarios, the blocks deceleration is likely too gentle to trigger the Mold, and even it wasn't, it's a 50% trigger chance, not 100%.
3) In other scenarios, where the block isn't 10x10x10, if it even triggers at all, it triggers inside the goo of the GC.
4) In all scenarios, with absolutely no exceptions, the 1" cube area effect will not hit anyone outside the pit unless the Yellow Mold is not in the center, and if it's not in the center, it's at best going to hit two 5' squares, I guess maybe three if this isn't a corridor and it's on a corner. So it's likely to miss people.
Sorry for all the ALL CAPS but people are just completely ignoring how this is non-functional.