Oracle Text

Double strike

R: Char-Rumbler gets +1/+0 until end of turn.

Card Rulings

5/1/2007 Yes, Char-Rumbler’s printed power is -1. While its power is -1 or 0, it simply deals no combat damage.
5/1/2007 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.
5/1/2007 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.