It does give the opponent four life, but this downside is hardly impactful, especially considering you'll likely have a field full of creatures to take it away just as quickly as they got it
During play, you have one active Pokemon, and a bench full of backup critters
The original way to do this was to use any uncommon creature due to a lack of uncommon legends, however, we've seen so many more legendary creatures at uncommon that some groups prefer to use legends when playing the format
The 1/1 is value but it doesn't really make up a whole cards worth of value
Yes, you can attack a planeswalker using myriad tokens
Scars block introduced the MTG keyword Infect to the game - creatures with Infect deal damage to players in the form of Poison counters