Here's an idea:
When a player that week wins, they get the armor pieces sent to them in their mail. They are told of what they do, and have an option to "reject" it. For that week, the item is returned. Whoever is next in line will get a "silver" version of the costume sent in the mail with universal buffs in the same manner as the gold one's debuff. This encourages other players to still play well, and if players keep rejecting the mail it will slowly make its way down the line of Lockdown players, and benefit others to "overthrow" the original winner. This also means if you get the silver armor that you might be able to get a gold next week, thus stripping you of the silver armor boosts.

This allows players who want to be able to "brag" to not be put out of lockdown for a week(with those debuffs), and if they do reject the debuff then they are essentially buffing potential competition. The mails sent out are automatically deleted after one day, and thus players would be inclined to log in every Monday to see if they scored the costumes.

I'd recommend some graphic under the gold/silver player's character so others know of their status while fighting them.

However, someone might have a plan for later that week for a GvG and they want to have the best possible stats possible. They could possibly loose immunity due to this armor, which would directly affect their gameplay. Having a reject option for a week would also allow other players to be competitive with the top ranking player, and even dethrone them, but in the process become the #1 and lose the silver buffs.

If you can play well and are consistently scoring the highest amongst the lockdown community, then by all means you still have the bragging rights to hold onto that armor.
And as an idea, the "silver" armor would last a week from when it was acquired, hence there could be multiple silvers in the game at one time.

Players who can play great with debuffs are still rewarded for their good work. However, sometimes you need that extra CTR, or MSI, or ASI when faced with someone of similar skill and bonuses. If you know you are going to be going up against those people, or are going to be playing competitive games, then the option to not wear the armor (as it seems you want the costume to be auto-equipped) would be great.
The silver pass-along idea is just so someone gets to feel great, and at the same time potentially perform better than they usually would have for a week, and thus potentially get themselves to gold status to keep competition on.

how about make them cost 1 special token, as you said, but also make them cost 200-250 regular tokens?
maybe put a special crest on the special token ones

I understand your reasoning, but at the same time a person who wins one week might not want to have the armor or costume for whatever reason. The idea of giving the "next in line" person a costume that actually benefits them makes it harder for the person who rejected the gold armor to maintain the "gold" title, thus rotating the top player.

Also, something that might be good in general is for winners to get a crest accessory that would be bound to the player but could be worn across all armors always (infinite accessory) that, when inspected, would tell anyone inspecting how many times they had come in 1st, 2nd, or 3rd place in terms of weekly lockdown scores.

What I'm thinking is, instead of a silver armor costume (silver armor is a lockdown scoreboard thing. It is like buffing another player to overtake your score instead of taking the debuff yourself and show that you can prevail through debuffs. Either way, you are the champion that week, but you can reject the armor), maybe a bronze one. Bronze costumes would be in all standard accessories/armor designs, and have a shiny... Well, bronze color.
These would be costumes ONLY (would not affect lockdown, whereas gold and silver do), and would NOT be taken away at the end of the week if you didn't maintain your status. If you came in 3rd, 4th, or 5th place, you would get one Champion token. If you came in second, you would get two. If you came in first, you would get three. These tokens could be exchanged for costumes. Costumes would be automatically bound - however, maybe there would be super expensive versions that are unbound? The descriptions would be altered at the end to read "This costume is bound to its champion, showing their valiant victories in King Krogmo's coliseum." if it were bound, and read "This costume is unbound to it's champion, showing the charitable character of a knight who continuously shines in King Krogmo's coliseum."

Make the unbound costumes cost at least 50 tokens. In this way, it would take a little over 4 months of staying in first place to even buy a single bronze item to sell, and would make playing PvP a potential way to get good money. Unbound accessories and bound costumes could be 10 tokens, meaning if you top in the 1st three times that month and make it to at least 5th the last one, you'll be able to get that accessory. Bound accessories would be 2 tokens.

The gold and silver sets could both do the same things in terms of debuffs, but maybe the silver one doesn't penalize MSI, CTR, freeze, curse, and fire statuses. If you accept the sets you would get +2 champion tokens for gold, and +1 for silver. All top 5 contestants would get +1 champion token.

Oh! And maybe we could have it so these tokens could buy those super rare bombhead masks! And maybe have bombhead armors to go along with them. That would be a cool addition.

And perhaps instead of the sets being anything, it would simply give them a prismatic sunshine aura in lockdown, and the golden costume is something that happens outside of lockdown. That way you can make out who was #1 while in-game while still knowing that they're wearing full snarbolax. Silver would have a prismatic snowfall aura. Both costume pieces have these auras built into them as well, so you can show them off.

Bronze costumes would basically be a way of saying "Hey, I was on the lockdown scoreboards!" rather than "I played lockdown a lot". I'm still of the idea that we should have krogmo prize boxes we can buy with krogmo coins year-round, with the 1% chance being bombhead masks or an explosive aura. Heck, perhaps have a 5% chance at a copper item that looks almost identical to a bronze one, but a bit more red.