General thinking about magic spells and tiers.
Tier 0 spells aren't very effective in the sense of them costing more than others and taking more effort for less gain. Think along the lines of candle flames, 1lb telekinesis, or Cure Lesser Wounds (at best). It's what a small child or untrained power user would do before training or teaching. They're the Least powers, which are below "Lesser" on the scale.
Tier 1 and 2 spells are beginner-level spells. They cover the range from Lesser to Minor Powers, tending towards lesser. They are "autohit" spells because casters at this level tend to need to focus their energy on actually hitting what they aim at. A simple Potion of Death Resistance, an Ice Dart, or a Dispel Lesser Curse would fall under this category.
Tiers 3 and 4 are intermediate spells, or "average" spells. These are Minor to Normal Powers, tending towards normal. At this point, offensive users can choose to trust their own magical aim for more damage or use the controlled spells for a guaranteed hit. A Potion of Death Immunity, a Potion of Lesser Invulnerability, a Mage Shield, a third-level armor or second-level item/weapon enchantment, Mass Raise Vermin, or a Cure Moderate Wounds would be on this level.
Tier 5 is normal to major spells, or simply put "any spell that is not Tier 4 or a Tier 6." Cure Serious Wounds, a Potion of Invulnerability, Invoke Skeletal Abomination, a seventh-level armor or fourth-level armor/item, a Major Counterspell, or Minor Planar Gate are in this tier.
Tier 6 powers are the low half of Greater Powers. These are things like Mass Raise Dead, Firestorm, Mass Bless, Lesser Quicksand, Baleful Polymorph, Breath of the Grave, Greater Counterspell, Planar Gate, or a ninth-level armor enchant or a fifth-level weapon enchant. Tier 7 powers are the upper half, and would be Mass Raise Hungry Dead, Inferno, Mass Mage Shield, Forced Transformation, Death Fog, Greater Reflect (known as the "Fuck you right back" of the magical world), Invoke Angel / Invoke Demon, and a 11th-level armor enchant / 6th-level weapon enchant.
Tier 8 and Tier 9 are the low and high half of master-level powers. These would be 18th-level armor enchants/10th level weapon enchants, Quicksand, Napalm, Elemental Undead, etc.
Tier 10 and above are Oneness, verging on Wizardry. Think "Mass True Resurrect", "Invoke Greater Angel/Demon", "Permanent Immunity to X", "Perma-orbit", "Teleport", "Mass Instakill", "Wish", "Dragonfire AoE" etc.
Obviously, costs vary. Morgred and Neun can hit a Tier 10 spell for 30 MP; while if they were to try to make an 11th-level weapon enchantment, it'd drain at least 115 MP. Unsurprisingly, I advise playing to your strengths and not casting a spell that would straight-up kill you.