DeGrom (elbow) threw a bullpen session Friday and mixed in some sliders, Kennedi Landry of MLB.com reports.
Friday marked deGrom's third bullpen session, but previously he had been limited to fastballs and changeups. It's unclear when the 35-year-old will come off the IL, but considering he'll likely need multiple rehab appearances, deGrom shouldn't be expected to make his season debut until some time in August.