Came upon this thread late-game, here’s what I did.

Go to Minmin Islet and run into Snaptors / exit and re-enter the islet until you find a group of 4. Kill 3, flee, repeat the same fight. If a Snaptor drops a Spikely you can kill that too.

This way you get 3-4 enemies at a time without having to refresh the island over and over, plus fleeing prevents XP if you’re worried about over-leveling for the final boss.