Can I use Dragons Rage in a showdown?

No, you cannot use Dragon's Rage during a showdown.

According to the rules for showdowns and the card's text:

1. Showdown Timing: During a showdown, you are restricted to playing spells or activating abilities that are specifically labeled as Action or Reaction (Rule 347).
2. Card Classification: Dragon's Rage is a spell, but it lacks the Action or Reaction keyword. Therefore, it is not "legally timed" for use during a showdown.

This is consistent with RiftJudge FAQ #7488, which explicitly states: "Dragon's Rage cannot be played in combat because it does not say action or reaction on it."