FFXIV is too simplistic and bland

[ADVSS]

Linked mobs in the overworld seem to be solely based on your strength relative to the thing you're attacking. Fight something of similar level to your own and it's always a single fight. Attack something of a lower level and it will also draw the next closest enemy to the one you attacked.

I imagine it's something like that attacking something draws enmity, and a sufficiently strong attack creates more than 100% enmity and that "overflows" to the next nearest enemy. Do it in a really low-level area and you'll draw an entire pack.

Having your chocobo summoned also seems to affect whether you get this overflow effect.

You can literally see mobs that are linked together with a faint golden line that blinks slowly.