The first extra combat card printed was Relentless AssaultRelentless Assault in 1997
While a 5/5 with hexproof is solid, if its owner controls their commander, Stromsurge Kraken gets +2/+2 and gains the added benefit of drawing its controller two cards whenever it becomes blocked
The other two are Goldbug, Humanitys Ally/Goldbug, Scrappy Scout and Flamewar, Brash Veteran and Flamewar, Streetwise Operative
It is the place where you can try out your crazy six card combo and even if you dont pull it off, you can still have fun trying something that would not be possible in any other format
These are mostly black designs, considering the selfish nature of the symbiote carriers, and as a mechanical tie-in, some symbiotes allow you to exile creatures from your graveyard and turn them into +1/+1 counters, similar to how scavenge works