Char-Rumbler — ruling 1

Because Char-Rumber's power is normally negative, you'll have to give it at least +2/+0 before it'll deal damage. It won't deal negative damage.

Char-Rumbler — ruling 2

Yes, Char-Rumbler's printed power is -1. While its power is -1 or 0, it simply deals no combat damage.

Char-Rumbler — ruling 3

A first strike damage step will be created if Char-Rumbler is in combat, even if its power is 0 or less. The normal combat damage step will follow.

Char-Rumbler — ruling 4

If Char-Rumbler's power changes between the assignment of first-strike combat damage and the assignment of normal combat damage, Char-Rumbler will deal a different amount of damage in each combat damage step.

Char-Rumbler : règles, fonctionnement et interactions (MTG)

Char-Rumbler is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Double strike : This creature gets +1/+0 until end of turn.

How it works : Char-Rumbler

Original English text — Wizards of the Coast / Scryfall

#1March 19, 2021· Wizards of the Coast
Because Char-Rumber's power is normally negative, you'll have to give it at least +2/+0 before it'll deal damage. It won't deal negative damage.
No other card is named in this ruling.
#2May 1, 2007· Wizards of the Coast
Yes, Char-Rumbler's printed power is -1. While its power is -1 or 0, it simply deals no combat damage.
No other card is named in this ruling.
#3May 1, 2007· Wizards of the Coast
A first strike damage step will be created if Char-Rumbler is in combat, even if its power is 0 or less. The normal combat damage step will follow.
No other card is named in this ruling.
#4May 1, 2007· Wizards of the Coast
If Char-Rumbler's power changes between the assignment of first-strike combat damage and the assignment of normal combat damage, Char-Rumbler will deal a different amount of damage in each combat damage step.
No other card is named in this ruling.