Then it might be a bit OP... this makes lots spam decks unkillable... from the simplest FFQ to scarab spam/RoL hope. Even RoF can't dispose of those properly with the addition of this card (AND the upgraded version costs nothing!) Most CC are nerfed then, while this card buffs devour. Think of an oty that has double growth rate.
I would have preferred heal instead of add hp.
Not really. It takes 3 turns for an RoL and 2 turns for Firefly to outgrow RoF, which is 3 damage. The only card this can immediately counter is Thunderstorm, which is already pretty weak by itself.
As for Otyugh, it's only a matter of time before you can capably Devour everything on the field.
Blessing makes upped Otyugh 3 | 8 for 2
5
+ 2 cards + 0 turns.
Osmosis makes upped Otyugh 0 | 8 for 5
+ 2 cards + 2 turns.
Overall, Osmosis is slower to start up but has greater long-term potential. Rush decks are likely to be vulnerable to upped Otyugh itself and Blessing makes Otyugh more immediately stronger, which would probably be preferred unless the creature in question is not a threat for at least 1 or 2 turns after an Otyugh/Osmosis combo hits the field. IMHO, Osmosis works better with cards like Gravity Shield, Acceleration, and Liquid Shadow that use HP as a drawback/defensive method instead of an offensive method (combos such as Otyugh/Osmosis are viable in some situations such as limited deckbuilding or a
/
Control rush.)