Migosp is a cheap card with the ability to give +2 HP to a random ally monster when placed.
As such, it's recommended you have at least one other card on the field before deploying Migosp as to not let its ability go to waste.
It's even better used early game, as 2nd monster placed while your first one is still alive.
After all, this card isn't really useful mid- to late game due to its weak stats, and because you probably have more monsters on the field by then, the effect is more random.
Because of this, you can better use it's upgraded/Hard Mode version Migospel at that point, as Migospel can give +3 HP to a monster of your choice.