Amass can be built like a weird Voltron deck where you focus on making one big creature, but the mechanic also says make a token, which can be sacrificed repeatedly, and thats where Warbeast comes in
They are basically a Chromatic Star that finds a land and continues to fix for you in future turns
This gives you the perfect incentive to keep using her to get back your songs and keep recycling resources
Its first ability doubles the mana output of your nonland permanents, which includes all your mana rocks and dorks like Midnight Clock and Llanowar Elves
It can be devastating depending on the target you choose, be it Phyrexian Obliterator or Screaming Nemesis
However, if youre deep on Sun Titan, Sevinnes Reclamation et al, then you can more confidently cast this early