The Runic Colossus is a gargantuan construct from Bigby Presents: Glory of the Giants. The creature designers for Bigby’s seem to have settled on a theme for the creatures they created for the book. They eschewed the use of Legendary Actions to give the family-sized monsters they were creating more opportunities to deal damage, and instead focused on giving creatures very powerful attacks. They might not hit often, but when they do, the player knows it. These creatures are slow but devastating. These creature end up with more reactions as well.
Speaking of reactions, the Runic Colossus reaction is probably my favorite part of the stat block. When a spell is cast on the colossus, it can use its reaction to make ranged spell attack on the caster. If the attack is a success, the spell is countered, and the caster takes force damage. Sadly, it has a limited number of uses of this reaction each day.
Oddly enough, the lore on this creature states that the giants of old created the Runic Colossus to battle dragons. This reactions seems like an odd choice for a creation focused on battling dragons. Their stat blocks don’t typically include casting. Maybe they were having problems with gem dragons, who are more likely to be spellcasters? It’s regular attacks are melee attacks, which also isn’t optimal for dealing with dragons. I guess that’s what its beam weapon is for…
Runic Colossus: Not a Bright Boy
The Runic Colossus’s dump stats are Intelligence and Charisma. This makes it prone to magics that will stun or incapacitate it. Fortunately, its immune to pyschic damage. The other good news is that the colossus has buckets of Hit Points to withstand the attacks it will take while incapacitated.
The Runic Colossus is great, but not quite strong enough to make my list of the strongest D&D monsters.