If you are looking at the natures warrior and/or the summoning of crocs for them to run into, it sounds like you may have your mind up as far as the style of the encounter goes... But let me bounce an idea off you real quick for a slightly different style...
Using the Barb1 + Druids Wildstride + Natural Terrain for a Lizardman, you've got abilities that will let you move through the swamp with absolutely no hindrance whatsover - as opposed to the party, unless they start wasting fly spells, etc.
Have the druid pop out of -literally- no where, hurl a single spell (SNA is great, others like entangle also rock), and then dissappear back into the marsh. With any luck, the high spot char will see him running away and make to follow... With a little effort on the druids part, this whole combat scene can turn into a long guerrilla style combat with the druid sniping, running, and leaving nasty ambushes (SNA, charmed animals, animal friends, etc.) behind as he runs away.
Not to mention, he can lure the party to some of the nastier denizens of the swamp (natural crocs, etc.) with relative ease once the party knows there is an enemy hiding out in these here parts

. Natural terrain will also be the source of endless discomfort from bugs (ever been in a -real-thick swamp? Once you start sweating, you're a fricking smorgasboard to all the insects!)
Run it like a Viet Cong vs American Infantry running fight through the thicks of the swamp. By the end of the day, the druid, whose been conserving his spells, can concentrate on the party and give them an extremely rough time during the evening, robbing them of spells (no rest = no spells) for the morrow. Summon Swarm, SNA, or even just ask some local animals (snakes in the bedrolls?) to come visit
Then let them see the dragon on the second day... They'll freak with little or no magic support

. 'Course, don't throw that dragon at them right then - that would probably be a TPK... Then harass them all day long with the lizardman shaman running guerrilla style warfare again

.
Just a little different style, and now you can 'pull' punches and fudge dice/tactics whenever necessary to re-enforce the 'difficulty' class to the precise degree you want, without unnecessarily risking the party (unless they do something insane, like see dragon, cast flight, and pursue... with no spells, no buffs... they would deserve to lose that fight!)
On the second day, the lizardman shaman can 'lure' them to the black dragons lair to dispose of them - just be sure to have him fubar the lure to the point the players do figure it out in time to camp... The shaman leaves, figuring they are kaput from the dragon, but they have time to sleep, prep, etc. for the dragon.
Run that jungle/swamp combat right to the narrow edge of life/death for them - they'll not likely forget... throw in some off the wall tactics (SNA - Crocodile, 20' UP the tree.... drops down on party

etc.) for even more memorability.
Change off the standard tactic of 'heres combat, heres bbeg, kill him' to 'heres combat, heres bbeg, heres BIG bbeg, survive the first well enough to tackle the second, then kill the first!'
Just an idea !
Oh, and for Komodo Dragons, WotC posted a thing sometime ago - use the monitor lizard stats, change the description, and advance the monster per the MM rules until desired size is reached.
Freaks out players to fight Komodo Dragons in swamps... 'specially 10' long ones
As to the offtopic - all I have to say is the same as someones sig around here - "The rules should serve the game, the game should not serve the rules"...