A video of Mr Siddaramaiah's near-perfect mimicry at the rally has become a big hit online.
The Karnataka Chief Minister, campaigning for polls next year in the state, targeted PM Modi on the promise to bring back black or untaxed money stashed abroad and mocked most of his popular catchphrases to drive home the message.
"Sabka saath, sabka vikas (Development for all)," boomed Mr Siddaramaiah in the middle of his speech. Pause. "What development?" he wondered, switching back to Kannada.
"Acche din aaega," Mr Siddaramaiah sneered. "Kab aayega? Kisko aayega? (Good times are ahead? When? For whom?)"
"Achhe din aane waale hain" ("Good times are ahead") was the BJP's popular slogan during the 2014 general election.
"No acche din, no vikas, no Rs 15 lakh in your accounts," the minister jeered.
Mr Siddaramaiah also targeted state BJP president and former Chief Minister BS Yeddyurappa, who had spoken about development at a rally in the same town earlier.
"Election brings out so many hidden talents. Amazing," joked blogger and commentator Sandip Ghose on Twitter.
"So clearly he thinks Modi's popularity can cost him the state else wouldn't have bothered countering," tweeted Shilpi Tewari.