Herald from Dominion Guilds says that you can over pay for it and if you do, you may put X Action cards from your discard on top of your deck, where X is the amount you overpaid.
Can you place Herald on top of your deck if you overpay?
(Note: This question comes down to a matter of timing. Does the "when you buy this" clause occur before or after you place Hearld in the discard pile)
No, Herald cannot put itself on top of the deck by overpaying.
From the designer, Donald X. Vaccarino on BGG.
Q: OK, so when the "when buy" effect kicks in, is the herald you just bought in the discard pile yet? Or would it have to be a "when gain" like Inn to do that? i.e., can you pay 5 to buy a herald and put it on top?
A: When-buy, which includes overpay, triggers before gaining, so you can't buy a Herald and use its overpay to put that very Herald on top of your deck.
