{Ajani mentor of heroes} + {Ajani caller of the pride} + {Purphoros god of the forge}
~100 cats
200 damage
If your opponent lets you ulti 2 ajani's then they deserve to lose. On a side note you would have to ulti the nyx ajani then summon caller of the pride after.
It's green and red, plenty of ways to get mana of whatever color in large quantities.
And I mean you could throw in {Doubling Season} to just instant ultimate both them.
Meanwhile purphoros is just like oh hey! You're all dead!
There's always the easier way of Nyx Ajani+{Sanguine Bond}
Or just you know, {Door to nothingness}