This is in the realm of Bukkit plugin development that I'm not familiar with (probably would involve ProtocolLib), plus I'm busy now, so I'm tossing this idea out and wondering if it would work or if anyone wants to make a plugin for it. When a player mines a block, cracks appear in it before it breaks. With this plugin, after an initial threshold, the "damage" on the block stays there even after the player stops mining it, and the cracks remain, serving as a cool visual effect. Also, explosions damage blocks around it that are not completely destroyed, leaving cracks in them. More cracks on closer blocks, fewer on farther ones. That would be really cool to see and would probably give me a new reason to go around blowing stuff up on my server. It would also be cool if the cracked blocks would take less time to mine and be easier to destroy with explosions, but I understand that that would involve a database and a lot of extra processing!