The "121" is not an official Mojang version number. Instead, it serves three critical purposes in the unblocked gaming community:
Unlike web-based clones (like ClassiCube), Eaglercraft supports nearly all redstone components: Repeaters, Comparators, Pistons, and Hoppers. You can build functional calculators and flying machines. eaglercraft unblocked 121
Do not search for "Eaglercraft 121 download" on Google. Most top results are viruses or survey scams. The legitimate version is a single HTML file (roughly 20-30 MB). Look for: The "121" is not an official Mojang version number
The best reason to play version 121 is the thriving underground multiplayer community. Because official Minecraft servers block bots and cracked clients, the Eaglercraft community has built their own servers. eaglercraft unblocked 121