Something to note is the comments on stickers in Legacy:

The rise in popularity and competitiveness of ________ Goblin is, however, an issue for tabletop play. While it is acceptable for the player that is opting into the Goblins deck and the requirement of bringing a sticker deck to accommodate ________ Goblin, it puts pressure on all opponents to also bring a sticker deck. This is because a player can bluff or represent a deck that requires stickers at the start of the match, but also cards like Phyrexian Metamorph or Phantasmal Image would likely want to copy ________ Goblin to net a bunch of mana and you must have a sticker deck to get that ability. “Neither of these things are ideal,” Musser said. “We are aware of it. It is an in-paper issue only, but it is something that we are currently in search of a solution for. I think we can promise by the next [B&R] window we will have a solution.”