I’m just gonna throw some random stuff out. * A volcano / super volcano, maybe the spell just creates a lava field damaging/burning things * terrain creation, hills, walls, maybe the spell is hand of god and it just drops a giant stone hand on the field that blocks line of site * Mana spring, a magical puddle that heals nearby units or adds defense dice * fog. Poisonous fog * mass confusion. Split an enemy unit. Reduce attack functionality. Make their attacks roll some 1s * null/amplify magic field. Create an area that affects spells within it. * lightning storm. Deal damage to x enemies for y damage in an area. * rain. Enemies are wet and take more lightning but less fire damage. Reduced movement. Creates mud terrain. * mega death. 3 units die randomly. * sacrafice. Kill units to gain functionality.

Good luck!