We consider a model of inflation in which the inflaton field is a rolling axion with a potential which is flat enough to support an intermediate phase of ultraslow-roll (USR) inflation. Because of the Chern-Simons interaction, one polarization of the gauge field experiences the tachyonic growth during the first slow-roll stage, inducing large corrections in curvature perturbations via the inverse decay effect. A nontrivial feature of our setup is that, once the system enters the USR phase, the instability parameter falls off rapidly, terminating the gauge field production efficiently. Consequently, the power spectrum involves two separate peaks; the first peak is induced by the gauge field particle production, while the second peak is due to the standard USR mechanism. We show that the power spectrum at the intermediate scales develops strong scale dependence $\propto k^m$ with the index $m>4$. Calculating the bispectrum, we demonstrate that non-Gaussianities with nontrivial shapes and multiple peaks are generated in this setup.

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• Inflation