As the name suggests, this ROM hack replaces Mario with Sonic, with the rest of the game left relatively untouched. Sonic always runs, regardless of whether or not you're holding the B button, all of the texts are changed from Mario to Sonic and Toad now gives you a useful tip.
This ROM hack is an .ips patch file, so you'll need Lunar IPS to apply this patch to your Super Mario Bros. ROM. The patch works for both Europe and Japan/USA regions.
Country: Japan/USA
CRC32 C96971E2
MD5 D7176817CDE28CE3F6589B5E833089A4
SHA-1 F77562C2A3274B0DD0379ED3F2D1ADDA340520E6
SHA-256 E37080256BACC4FB14182799D4929F53A38E9D8410029B394D9293F8B77AB4AF
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Country: Europe
CRC32 9A2DB086
MD5 BA39DDE63AB209B1BC751E0535E72B18
SHA-1 0C4992FC08D2278697339D3B48066E7B5F943598
SHA-256 EC299B990E8BFEE8BA46E3F61D63B2E1AE5B8A2E431DE84E2E4BBD692DC53586