Instigator Gang grants +1/+0 to all attackers and transforms into Wildblood Pack, which grants +3/+0 to all your attackers
The game expects you to ramp into this attack with cards like the Baby Pokmon (whose attack attaches Energy to your bench for free) and Ho-oh ex (whose attack generates exactly the three Energy types needed by Lugia), since the game's random Energy generation means that just being able to use it once without these effects is a pipe dream at best, and only getting it off a single time probably won't even win the game
But I also think the range of reasons is much broader than the least charitable view
There are tons of ways to use it to make infinite mana, with Vizier of Remedies, Swift Reconfiguration, and Solemnity coming to mind
Grasp the role of mana as a resource, its generation through land cards, and how it is utilized for casting spells
Its only effect is an ETB trigger that lasts just for one turn