Tenser's Transformation

Level: 6th
School: Transmutation
Casting Time: 1 action
Range: Self
Components: V, S, M (a few hairs from a bull)
Duration: Concentration, up to 10 minutes

Description:

You endow yourself with martial prowess fueled by magic. Until the spell ends, you can’t cast spells, and you gain the following benefits:

• Bonus to Attack Rolls: You gain 50 temporary hit points. If any of these remain when the spell ends, they are lost.
• Extra Attacks: You have advantage on attack rolls you make with simple and martial weapons.
• Weapon Proficiency: You gain proficiency with all armor, shields, simple weapons, and martial weapons.
• Extra Attack: You can attack twice, instead of once, when you take the Attack action on your turn. You ignore this benefit if you already have a feature that gives you extra attacks.
• Force Damage: Your weapon attacks deal an extra 2d12 force damage on a hit.
• Saving Throw Proficiency: You gain proficiency in Strength and Constitution saving throws.
• Endurance: You have advantage on Constitution saving throws you make to maintain concentration on a spell.

End of the Spell:

When the spell ends, you must succeed on a DC 15 Constitution saving throw or suffer one level of exhaustion.

Notes:

• Martial Boost: This spell turns a spellcaster into a formidable melee combatant for a short time.
• High Risk, High Reward: The additional force damage and extra attacks make you very deadly, but the risk of exhaustion at the end of the spell adds a significant drawback.
• Concentration Required: Requires concentration, meaning that sustaining it in a prolonged battle may be challenging.
• No Spellcasting: The inability to cast spells while this spell is active forces a change in typical spellcaster playstyle.

Source: Xanathar's Guide to Everything