Dome Fossil (MD 89). Fossils can’t be played during setup phase and create a mulligan even though they have to be played. Per the Unleashed rulebook from 2010: „Fossil Trainer cards: These are a special kind of Trainer card, that act like Basic Pokémon when put into play. When that kind of Trainer card is in your hand, deck, or discard pile, it is not considered a Basic Pokémon. However, these Trainer cards always count as Basic Pokémon during set-up.“
Not sure if they are bugged in other formats as well but might be worth checking out other dpp and hgss formats.
Thank you!
------------------Begin Game Log------------------
The game is about to start
Type: QuickPlay
Format: 2010 (DP–UL)
Battle begins between GWood and Homselus!
GWood will take additional mulligan(s) after Homselus sets up to play.
Mulligan phase: GWood took 14 additional mulligans
Homselus drew 14 extra cards.
Coin flip [Opening Flip]: HEADS
GWood will start
Game setup complete
Between turns
Turn 1 begins
GWood drew 1 card
Homselus wins the game! Opponent surrendered
[Homselus]: Homselus has exited game.