Simply look at your moves type, then figure out the damage multiplier separately for both of the opponents types, then multiply the two multiplers together
The Supporter Trainer card may not be as highly valued as Giovanni would think it should be, but it still makes this list as one of the top cards in the Pokmon TCG: 151 set
Your only other Monster searcher
Plus, you wont risk damaging your precious cards with a DIY gone wrong
We don't expect to see Sunscour follow the same path, but it's notable how good 'free' spells, which require you to pitch a card to get their effect, have become in recent years
However, I think its pretty fancy and shows a certain level of skill if you hold cards that allow you to counter Vigilance when required in your deck