Tactics for playing against Sylvan.

I wouldn't say it's absolutely necessary to push them all the way to the portal; besides, it can appear quite early, and it doesn't require much to summon. The portal doesn't give them a decisive advantage. Water elementals can only be purchased for defending the castle, as they significantly slow down the hero. If you want to use them in battle, acquire the appropriate summon. But mantises are quite suitable for the army. And who else? I don't see any other candidates from the portal...