This card is just too cheap, make it a spell.
This and rewind can destroy any unprotected creature for 3-5 . Depends on rewind source.
If the opponent has no creature, it can still shrink their deck, quite possibly messing up their deck strategy totally.
Result: this card will be in any deck. Only a played sanctuary protects from it.
Since the goal is to shrink the opponent's deck as a strategy, a spell would not do.
Examined at the bottom.
Yes it can mess up their deck with a large quanta investment. So can any disruptive strategy.
Result: This will be in any (time denial deck, time deckout or time control), not a (time rush, time OTK, time charge).
Hieroglyph + Rewind
Casting Cost: 4|3
+ 1 card
Activation Cost: 2
+ 2|1
+ 1 card (equivalent to 4|3
+ 1 card)
Benefit: Instant kill
Arctic Octopus + Shockwave
Casting Cost: 3|3
+ 1 card
Activation Cost: 2
+ 2|1
+ 1 card (equivalent to 5|4
+ 1 card)
Benefit: Instant kill, 1 attack
Direct comparison:
AO + S: Costs 1|0 to cast, has +1 attack (typically worth an extra +1 casting cost)
H + R: Costs 1 less to activate
They are balanced.