During the initial mint, free Burn-Rerolls was activated. This means that during mint, if you didn't like the trait combination of your Mike, you can activate burn-reroll which allows you to send your Mike to Hell (burn) and mint another Mike in one single transaction. Activating burn-reroll essentially reduces the circulating supply of Mike NFTs, hence the reason why there are only 2637 active Mikes currently.
Note: Burn Rerolls for Matic Mike has ended since all 10,000 Mikes have been minted.
Burn-rerolls for Evil Club Lords (ECL) work similarly, except this time there is a payment of 10 HGH and a maximum of 10 burn-rerolls per ECL