This mod is part of The Vanilla Experience.
A minimalistic configurable mod that allows Shulkers to drop two or more shells, up to 64. It'll use the normal drop chance of shells by default. This means that the amount of shells dropped will only be altered if one would've dropped without the mod. You may also enable an option in the configuration page to make Shulkers always drop their shell and ignore the drop chance entirely.
The configuration page