A season is the ten weeks that new Arks are released with each Online mission. There’s only one new ark per OM
Occasionally, there is an extra week thrown in with an Ark that can be collected multiple times but otherwise, rules for the online missions apply to all weeks
Season 1: Shadowstalker: Allows you to set the pace for the game. And its a rare combination of deadly offense and defense. Very hard to get rid of especially when reinforced/bolstered. MVP quality ark.
Season 2: Triphoon: A bit easier to kill than the SS. But has more offensive capabilities. Everytime you heal its life-bar from nearly nothing, its like having another ark, which is a winning advantage, all other things being equal.
Season 3: Can’t really say right now, Cyberwurm is a great ark and am tempted to pencil it here, but one can truly know until the season is over.