The interface issue that constantly trips me up is taking monsters off the map portion of the board and putting them in an investigators play area to show shes engaged (this is an issue in various Fantasy Flight ranging from this to Marvel Champions)
The Team Up set is from Sun & Moon era, released all the way back in 2019 (which doesn't actually seem that long ago!)
You can certainly run this Balrog as your commander and do Dargo tricks, but I think it works just fine as a card in your 99 and played fairly, especially if you have ways to bring creatures back from the graveyard
If this card is Normal or Special Summoned: You can Special Summon 1 Level 4 or lower "Goblin" monster from your Deck
It does mean that if cards like these are the only way your deck can win, you probably need to examine your underlying strategies to assess why they arent pulling their weight
It can't be the target of Sorceress's Schemes, which reads in part "Return target instant or sorcery card from your graveyard or exiled card with flashback you own to your hand." (6/6/2025) When playing a card as an Adventure, use the alternative characteristics and ignore all of the card's normal characteristics