Regarding the swamps, here's a race – if you can't come up with a name, don't write nonsense!! Use decent expressions!! (can't think of a name):

1). Mosquito - Plague Mosquito (Infects with plague). High speed and initiative. Huge growth rate, but very weak in strength.
2). Troglodyte - Don't remember the name in Heroes 3 (Blindness doesn't work, can emit poisonous fumes that have a chance to weaken the enemy). Normal growth rate. Low speed and initiative.
3). Beehive (casts the Hornet Swarm spell).
4). Giant Leeches (can stun a unit for 1 turn due to severe blood loss).
5). Belchoer (random cast). Ranged attacker. Initiative 10, speed 4.
6). Please use more appropriate language Horrible monster that inspires fear not so much with its strength, but with the stench emanating from it (fear - the enemy runs away 3 tiles (% chance on hit), slow - reduces the speed of creatures by 2 within a radius of 3 tiles from it (it's difficult to move in such a stench)).
7) Cthulhu - Cthulhu Lord. A giant octopus-mutant raised from the depths by sophisticated magic (immune to any weakening spells, can swallow (devour) any enemy unit for one turn, then spit it out, reducing its health by 1-5 (depending on the number of Cthulhus)).

They worship ancient gods who ruled the land long before the current races appeared, but then disappeared into nowhere.