Effects that modify an affected creature's power and/or toughness without setting them to specific values will apply no matter when those effects began
They're the key cards in the infamous Tron Modern archetype, which relies on their absurd mana ramp potential to bring out scary threats way ahead of schedule
It's only useful if A) your opponent attacked you B) it survives your opponents turn and C) you are happy to make plays during your MP2 instead of MP1
Similarly, this set leans less on its Trainer cards but brings back items like the Snatch Arm, now renamed to Grabber, which can let you snatch an opponents Pokmon right from their hand and place it back into their deck
The system, overall, is now more useful as a tool for tailoring your games
Combined, this collection does for Generation 5 what 151 did for Generation Wun (1)