Spoiler for Hidden:
the upped Tombstone seems a little bit too cheap comparatively to the unupped version
especially it costs random quantum.
what if there is already a creature at target slot?
does tombstone still affects the creature?
Yeah, after thinking about, getting possibly four first turn Tombstones with one Nova is a bit OP, how much should I raise the cost though? 5 
? I don't want to force a duo with 
, since essentially making certain creatures immortal (may be a problem with powerful creatures like Otyugh, since they rely on HP, not attack) gives many possible combos.
If a creature is already on the slot, it's still affected. But, the point of this mechanic is to be proactive instead of reactive, which EtG currently is.
1 = 3
3 = 12
my personal view though.
i think players will use it frequently to debuff opponent strong creatures,
which im not sure is it what you are planning as
my first sight is that you are trying summon creature with powerful skill
and protect it with Tombstone.
Actually, I planned on both uses being used, kind of how Rage Pot is used both offensively and defensively. You can essentially get rid of powerful enemy attackers, but you can also protect creatures that don't rely on their attack and instead rely on ability (ie. Fallen Druid, FFQ, Pharaoh). It's basically a Quint/Mutation.
As for costs, I don't think this warrants a 12
cost, the upped can still be used in Mono Death or Death duos/trios.
