are the creatures chosen randomly by the spell?
If they are, it would be really OP in two ways. After your opponent brings a monster:
1)
Summon a creature. Two balisk bloods, one for each. Annihilation.
Photons could be luciferned for massive hope shield.
And the combo isn't really impossible to bring out. An earth mark alone, plus entrophy/light mix.
2)
Instantly kill ANY creature. If your creature was 0 cost, then it's even better.
Currently the only insta-kill is shockwave, and it's not so easy to carry out.
Even if it wasn't optional, it would be too much. This is basically a free kill for dragons and other heavy duty creatures.
Me no like