I expect this would mostly be used aggressively, rather than defensively. That is, declare attacks, and play Ensnare to stop them from blocking. In that way it turn standoffs into wins, in a way that a broad sweeper or targeted removal spell can't. Even when done during an opponent's combat it does more than buy one turn, because it means you're free to attack back on yours.
That said, I can't imagine it's good often enough to be worth running.
@fsecco Mentor combat maths in a format where you have to think about so many possible lines of play is the worst. Vintage was so much more fun before it was printed.
Back on-topic, I think tapping creatures is too narrow for a card slot. Sacrifice two islands to destroy two creatures would be interesting.
The main I mentioned the card because it can serve two roles defensively (although that could be really bad) and offensively for the reasons Brass Man mentioned.
On the topic of not being that great, Sudden Shock is a card that red gets splashed for, I thought that this card might be worth a look to fill the Sudden Shock niche, especially with green making its way into Mentor these days.