Cards like Arcades, The Strategist or Plagon, Lord of the Beach turn Charix into effectively a 17/17 for very little effort
What takes it up another level is the fact that later instances of Voidwalker can cast any card with a void counter on it, which makes it brilliant in any deck that can grant it haste and keep bringing it back
Eternalize is a tweaked version of embalm with two key differences
Dalek Drone Everyone loves a Ravenous Chupacabra
If these games go really slow, then some of these might be good at breaking those stalled boards, especially this Crystal
Note that I dont actually have a perfect answer: this is, according to Limitless data, an unfavorable matchup, although several Rapid Strike players have told me it was not that easy for them