Will there be a fifth hero?

[serafimvremeni]

Will there be a fifth hero?

[Banzai]

Doubtful since the game is finished and complete. There are mods however and there is stuff like the semi official "Downfall" expansion which gives a couple of new heroes and allows you to play as the bad guys as well.

[Dice_24K]

There are quite a LOT of mods for new characters. No, they're not as balanced (nor polished) like the main game's characters, but a lot of them tend to be fun.

https://steamcommunity.com/workshop/browse/?appid=646570&requiredtags%5B0%5D=Character&actualsort=trend&browsesort=trend&p=1&days=-1

Here's a search query that filters out for just characters. Make sure you grab the required prerequisites. Also, there are a few that aren't new characters but skins for the four vanilla heroes. If I have any recommendations on where to start, it would obviously be Downfall.

Speaking of Downfall, it is considered an "Expansion" and here's a search query for "expansions" for you:
https://steamcommunity.com/workshop/browse/?appid=646570&requiredtags%5B0%5D=Expansion&actualsort=trend&browsesort=trend&p=1&days=-1
Downfall aside, I recommend Gensokyo, Ruina and Hollow Nest. Full fledged acts for you to discover that come with events, new enemies and also spoilers for their respective games. The spoilers are out of context, so perhaps not as impactful, but just be wary.

[1.2M | Missingno.]

No, game is done and MegaCrit is working on a new project.

[pitiflauticus]

Install and play the Downfall mod. It's amazingly well done, relatively well balanced, has a TON of new content, multiple new characters, and it will keep you hooked for a hundred hours more, or longer... enjoy!

[LHGreen]

Nope.

[anarcher]

Try the Grift the Spire or Downfall mods, they're quite polished.

[CynosureTheTank]

Probably not since Mega Crit is working on something new. However there are many mods that add new characters, and while some aren't all that good I would recommend playing some. As several others have said, Downfall is a excellent one.