Ojama Yellow

id assume this is by virtue of the champion battle against wallace, but swampert still has more good matchups in that battle than sceptile, thanks to its ridiculous bulk and earthquake by level. also, only three of wallaces pokemon are actually weak against grass, and two of those pokemon weak to grass know blizzard and ice beam. not to mention mudkip, marshtomp or swampert dont have a single bad matchup throughout the entire game. there may be matchups where the line is a bit eh, such as against norman or brawly, but theyre not bad in said matchups. as opposed to the treecko line which gets horribly devastated by flannery and winona, and blaziken, which cant do shit in the last three gyms of the region.

marshtomps damage output may be a little lacking in the late marshtomp stages since it will be relying a lot on mud shot, but thats honestly the only part of the game where you may have a slight bit of trouble. evolve it to swampert and youre going to have to try to even lose your nuzlocke, to so say.

point taken

I honestly dont mean to say blaziken or sceptile are bad- theyre absolutely stellar in the roles they fulfill and probably are the best fire and grass types in gen III hoenn, respectively. swampert is just the best non-legendary water type in hoenn as well (got kyogre for competition), and...yeah, likely the best starter you could fetch in any core series game for a nuzlocke, period.