The official rules are as follows: (a) You may choose to pay [cost] rather than pay this spell's mana cost
Many Elves tap themselves to add a lot of mana, and Dionus gives you a chance to make that mana again while growing its stats
It makes beating sweepers trivial, and manifests creatures on its own, which can become cheap sources of huge lifegain with Mastery of the Unseen even when you never have time to activate it
Lion Heart Rating: 4/10 Two mana to equip for +2/+1 is a fairly good deal, and the high casting cost is mitigated by the fact that its capable of killing a creature on entering
Dont be surprised if Tatyova doesnt stick around for long, she tends to find herself falling to the hands of a removal spell more often than not
And sure, thats the case, but theyre still eminently useful and eminently valuable, as the blue version (which seeks out instants and sorceries) indicates