You can only use this effect of "Oafdragon Magician" once per turn
The offering rates for each individual card within these packs remain tied to their existing inclusion rates, but the presence of an extra slot means an additional chance to obtain rare cards with each eligible pull

Chansey #3Holo Rare $65.45 Chansey #69Common $6.51 Chansey #3Holo Rare $88.29 Chansey #3Holo Rare $21.81 Chansey #31Uncommon $24.15 Chansey #72Uncommon $8.48 Chansey #19Rare $6.38 Chansey #20Rare $4.48 Chansey #76Common $1.11 Chansey #69Common $2.56 Machop #57Common $0.21 Poliwhirl #24Uncommon $0.24 Magmar #20Uncommon $0.16 Blastoise EX #21Ultra Rare $6.25 Starmie BREAK #32Rare BREAK $2.58 Tangela #8Common $0.17 Voltorb #39Common $0.05 M Charizard EX #13Ultra Rare $46.02 Ponyta #19Common $0.07 Electrode #40Rare $0.26 Pokemon 2-Player Starter Set (Revised Base Set Reprint Run) $249.50 Base Set Theme Deck - "Blackout" (Revised Base Set Reprint Run) Base Set Theme Deck - "Zap!" (Revised Base Set Reprint Run) $499.95 Base Set Theme Deck - "Brushfire" (Revised Base Set Reprint Run) Base Set Theme Deck - "Overgrowth" (Revised Base Set Reprint Run) $685.00 Base Set Booster Pack [Revised Unlimited Edition] $786.87 Base Set Booster Box [Revised Unlimited Edition] Base Set 2 - 2-Player CD-ROM Starter Set $176.60

Exile up to one noncreature, nonland card from that player's graveyard
That said, maybe itll get some tribal support or something
Still, I think a model where 8 of them are printed 3 times on the sheet and the remaing 7 are printed 4 times better fits the raw data, both in terms of secret rares per box (0.73 according to this model) as well as in terms of the ratio between full art Trainers and secret rares