Rules/Restrictions:

Any race published is allowed. You can use the Customize Your Origin feature from *Tasha's Couldron of Everything*.   Any officially published Class by WotC is allowed as well as Optional Class Features. No Unearthed Arcana

If there is a circumstantial bonus, such as Assassinate or Haste, please show each step in damage calculation.  

No magic items, charms, blessings, or epic boons.   
Exeption regular: +1, +2, +3 weapons  

No, the "damage done" can't be to yourself.

You are on your own: there is no other PC nor an NPC. 

Take into account that you might not surprise the Tarrasque.

You do not have advantage by default. If you can generate some advantage for yourself, then you may do so.   Explain how you do it.  

Consider your [target](https://www.dndbeyond.com/monsters/tarrasque) to have AC 25; Skill Checks str(+10), dex(0), con(+10), int(-4), wis(0), cha(0); Saving Throws Str +10, Dex +0, Con+10, Int +5, Wis +9, Cha +9;

Damage Immunities: Fire, Poison; Bludgeoning, Piercing, and Slashing from Nonmagical Attacks   
Condition Immunities: Charmed, Frightened, Paralyzed, Poisoned   
Senses: Blindsight 120 ft., Passive Perception 10

Clarification: Even if they are not listed in this question, all abilities a Tarrasque has are at its disposal. [Link to the full Sheet](https://www.dndbeyond.com/monsters/tarrasque)   

You may have one non-combat round of setup outside the blindsight range of the Tarrasque. Longstride can be cast in advance.