So I know this is a long shot, and probably not good enough, but this card has a lot of interesting potential in the current vintage metagame. It seems to have a lot of potential though both against token strategies, and against shops.
First off, its a 3 mana creature, which is certainly playable costwise, downside its in green and white only, limiting the decks it can be played in. Perhaps something related to the Sylvan mentor builds of earlier this year? Its a 3/2 with First Strike, which shapes up very well against most shops creatures except ballista and ravager, and basically every non-TKS creature in white Eldrazi.
Now its triggered and static abilities that make it truly interesting to me. Being a 3/2 with first strike is particularly good vs mentor, and it not allowing the opponent to gang-block means attacking it straight into a mentor with a field of tokens has a high likelihood of it surviving the combat with just a mentor or just a token. A lot of the current mentor decks don't have many offensive instants that allow them to trigger prowess twice on our turn to even contest it resolving outside of force. Because this is an on-attack trigger, even if Mirri dies, you end up with a functionally unblockable army. This would alone would make the token mirror swing hugely in your favor because they can still only block a single creature.
Then you get its second ability, where they can only swing back with 1 creature at a time. This is particularly great when in the token mirror, as they are stuck attacking with 1 token or just a mentor, and you're free to make as many tokens and gang-block etc.
It has a lot of really interesting potential interactions, and potentially gives you an edge in the mentor mirror while having a card that also is not a blank textbox vs shops like pyroblast or flusterstorm is. While I dont expect this to make huge waves I certainly want to try it and see if it can realize its clear potential.