Here's the written guide on how to defeat the boss for those who prefer it:
LUURD LLDDR RRLUR DLURD RDRLU (now L onto the crab to hit it)
LDLLU RURUR RLLDR RDDDL LULLD RULDR ULDLD LRU (now R onto the crab to hit it)
RDRUR ULLUU RDLURU (now D onto the crab to hit it)