SN Helios: A Multiply Imaged Type II Supernova Opening Time-Delay Cosmography beyond redshift of 3

We report the discovery and spectroscopic confirmation of SN Helios, a strongly lensed, multiply imaged Type II supernova (SN) at z=3.34 behind the galaxy cluster RXC J0018.5+1626. The transient was identified as a red F150W-dropout source (F277W = 26.1 mag) in JWST/NIRCam imaging taken on 2026 July 3 for the VENUS survey, with no counterpart in 2024 December imaging. Director's Discretionary Time observations on 2026 August 17 added second-epoch NIRCam imaging and a deep NIRSpec prism spectrum. The spectrum shows a strong, spectrally resolved H α emission line (FWHM about 7900 km/s) with a P-Cygni absorption blueshifted by 8800 km/s, together with corresponding H β and He I λ 10830 features, establishing a hydrogen-rich photosphere at z=3.34. Template fits classify SN Helios as a Type II SN, and light-curve comparisons with well-studied local SNe II yield a phase of 27.5 plus or minus2.8 rest-frame days past B-band maximum. Independent cluster lens models magnify the observed image by μ about 10-20 and predict another image within 2-6 yr, offering a rare opportunity for a time-delay measurement of H 0 with a source at z>3. The host galaxy is undetected in deep rest-frame ultraviolet and optical imaging, in emission lines, and in ALMA 2 mm dust continuum, leaving a heavily obscured counterpart unlikely. Its de-lensed M UV-13 places it far below blank-field limits and adds support to an elevated core-collapse rate per unit star formation in ultra-faint galaxies. Without the multi-epoch data, SN Helios would masquerade as a convincing z about 16 Lyman-break galaxy, with galaxy-template fits strongly disfavoring any low-redshift solution even with multiple medium bands. Its spectrum thus provides an empirical SED template with which high-redshift searches can vet similar dropout candidates.