Transfer as Bonus analysis:
Transfer: Y Power to Damage, Min X
This bonus would make most of its cards effective power value 6 or lower (assuming Y is 2 and X is less than 6), rendering any card without power or attack abilities extremely risky to play, even moreso than the other damage clans. Not a worthwhile bonus.
Transfer: Y Damage to Power, Min X
This one is much better. Assuming Y=2, X=1, this bonus would make its clan similar to Ulu Watu
in stats. Giving them damage-focused abilities would help distance the two.
Transfer in theoretical combinations and match-ups:
Protection: If the stat to be lowered is protected, the transfer is negated, but if the raised stat is protected alone, the transfer would still work.
Copy: The transfer would work for the copier as well as the copied. The copier could find itself DRed by its own ability. Power reduction would be less of an issue, considering both cards would be hit.
Steal: Same as above, except the copied card keeps its base stats. TP>D cards would have a power advantage, while TD>P cards can take a loss like a DR.
Transfer Opp: Power to Damage (and the reverse)
Lower an opponent's stat, but give them a boost to the other. Simplified, these would be DRs that help the opponent win or PR that make it riskier to lose.
Transfer Opp: 3 Power to Damage, Min 6
Transfer Opp: 3 Damage to Power, Min 1