I loved that game so much; it was my Panzer General. With an awesome soundtrack.
I took the trouble of getting to scenario 4, to capture a battle with those #@%&! slimes.
Edit: Eat that wall of text, since the Discourse "details" function is as random as ever.
Betraying the one dogma all of the Japanese fantasy scene is based upon, you are going to have real troubles facing the gooey beasts. You better prepare by upgrading your hero to a higher class, thus gaining access to spells. But for that, you have to farm all the enemies you can from the first map until this scenario. Standard soldiers are helpless; horse riders can somehow escape the massacre, while hardly damaging the things. The real way to counter them is either earning access to Attack buff spells (a difference of a couple of points is enough to tilt a battle in the first Warsong), or rely upon the Priest's unarmed troops, which are strangly effective at mastering the blob menace.