The prestige experience against a Pound/Psychic Blissey without the best attackers
This is my prestige experience, the strategy:
Use a Poliwrath with Bubble/DP first, which is about 500 CP below the defending Blissey.
After you used the third DP, you should be about dodge Psychic, though it is optional, but pretty important about the rest of the battle.
Then, after you use two more DP, switch to a Pokémon (CP lower than Poliwrath) that almost faints, but can survive at least one Pound.
If you dodge after "the third DP", the second Psychic should come just after you switch the Pokémon. If it doesn't come, just spam the quick attacks of your current Pokémon, don't dodge.
Afterward, after the Pokémon receives Psychic, it should faint, then switch you Pokémon to a Counter/HB Ursaring (having a similar CP to Poliwrath) to finish the Blissey.
The strategy above costs about 78 seconds, not the best obviously, but it should give an easy 600–700 prestige.
The "after the third DP" dodge – advanced version for players who lack of potions:
Dodge if you are lack of Max/Hyper Potions, don't dodge if you are lack of (Super) Potions.
Answers
I haven't gotten enough candy to power up my C/D Machamp yet. If I need to prestige against a Blissey at the bottom of a gym, I use an Exeggutor just under Blissey with C/So or E/So. I have done it with two Exeggutors at half CP before, but it is really close on time so not worth it.
If you need to use more than one prestiger to get through a Blissey, you can get the same amount of prestige/attacker to use one strong attacker just under Blissey's CP.
Yesterday, I attacked a 3000 CP Blissey with ZH/HB using my 2100 CP Exeggutor with Conf/Solar, which fainted with over 30 seconds remaining and the Blissey's health in the red. My 2100 CP Vaporeon with WG/HP finished her off with around 10 seconds to spare (my 1900 CP Machamp with Count/DP would do so even faster) for 700 prestige points with only two attackers!
If the Blissey has a better defensive moveset (like Pound/DG) and I dodge poorly, my Exeggutor may faint with about 40 seconds left (and Blissey's health in the yellow), but the chance that my Vaporeon would faint too remains rather low.