Where are Bilerot, Frank and Rasta reappearing?
They were sold by GW, along with a rules insert, at a tournament event last year. The NAF has decided to declare them as official in tournaments from Feb 2017 forward (in fact, that's where I got the rules for them.)
How balanced would you say they are?
I don't think there's anything game-breaking about them:
Rasta Tailspike, Skaven Lineman
MA: 8 ST: 3 AG: 3 AV: 7
Skills: Loner, Catch, Extra Arms
Rasta is a Skaven Lineman (base price 50k) with +1 MA (30k), Catch (30k, a doubles), and Extra Arms (another 30k). Loner should reduce his cost a bit. He should be priced about 120k, but he's an overpriced catcher with no skills (other than ST3) to help him hold onto it.
Frank N. Stein, Flesh Golem
MA: 4 ST: 5 AG: 1 AV: 9
Skills: Loner, Break Tackle, Mighty Blow, Regeneration, Stand Firm, Thick Skull
Teams: Human, Necromantic, Undead
Base cost for a Flesh Golem is 110,000, so add +1 ST (50k), Break Tackle, and Mighty Blow (40k total), minus a bit for Loner. I think he's actually a bit overpriced, but he's a ST5 guy with no nega-trait, so I think he's pretty well balanced.
Bilerot Vomitflesh, Bloater
MA: 4 ST: 5 AG: 2 AV: 9
Skills: Loner, Dirty Player, Disturbing Presence, Foul Appearance
Teams: Chaos, Nurgle
Base price for a Nurgle Bloater is 110,000. Bilerot loses Nurgle's Rot (for some reason), but gets +1 ST (50k) and Dirty Player (20k). But let's be honest, who's going to be fouling with their ST5, 180k Star Player? Hopefully no one, unless the game is in the bag or you have bribes. Again, he's a little overpriced but for a ST5 player with no nega-trait, that's okay, I think.
I wouldn't have any compunctions about allowing these in my league. I might even say Bilerot automatically gets Nurgle's Rot IF he's playing for a Rotters team.