If you would roll one or more dice, instead roll that many dice plus one and ignore the lowest roll.

When Draco, The Dragon-Hearted attacks, Roll a d20.

1-9 | Put a +1/+1 counter on Draco, The Dragon- Hearted

10-18 | Put a +1/+1 counter on Draco, The Dragon- Hearted, it gains trample until the end of turn.

19-20 | Draco, The Dragon-Hearted becomes a Blue Dragon with base power 5/5, Trample, and Flying until the end of turn.