This is narrow in like three ways
It won't trigger for effects that aren't digivolution effects, such as BT4-011 [Agunimon]'s effect that treats a Tamer as a level 3 red Digimon or BT6-060 [Deputymon]'s effect that allows digivolution requirements to be ignored
Some of these may surprise you
If you have the likes of Articuno ex, Starmie ex, or Lapras ex, its definitely worth throwing them in here and using them
However, the first thing you'll notice with this card is that it can't do any damage, both moves it has, affect the discard pile or deck, so both moves have their use, but I don't know if I would make Bunnelby a mainstay in any deck that I would build
Most Stax plans fall into three big buckets: 1) Taxing effects (make spells and abilities cost more) These cards raise the price of doing business