1. I want to give combat buffs or debuffs for actions that play to the crowd, for both the PCs and their foes. Any fun suggestions?
You probably want to use skills. You could make all of these at-will powers, or encounter powers depending on how often you want them to be used, or you can keep them a mixed bag. You can also tweak them to make them more potent and turn them from at-will to encounter. You can remove DC's altogether and treat them like skill powers they can just use if they are trained. Or you can make them reliable in that if they fail with an encounter power skill check, they can try again later.
Arcana (hard DC) (minor action) (at-will): You add a visually appealing element to the next arcane attack you make during this turn. If you succeed, crowd cheers and you gain a +2/4/6 bonus to your damage roll.
Bluff (vs Insight) (minor action) (encounter): If you succeed, crowd cheers as you flourish your weapon, distracting your opponent, and you gain combat advantage against the target until the end of your turn.
Endurance (hard DC) (immediate reaction when bloodied) (at-will): When hit with a melee attack, you ignore the blood and the pain drawing nearer your opponent. If you succeed, crowd cheers for your display of toughness and you gain 3/6/9 temporary hit points.
Intimidate (moderate DC) (minor action) (encounter): You cow your opponent toward the stands. Target is pushed 2 squares and takes 5/10/15 damage from miscellaneous objects thrown at him by the crowd for his cowardice.
Diplomacy/Religion (moderate DC) (standard action) (encounter): Your words manage to get the crowd behind you. Your allies gain +1 attack and +2/4/6 bonus to damage rolls until the end of your next turn. Also one ally who can hear you can make a melee basic attack. Special: This power may be used only once during the encounter.
2. The dragonborn foes have the opportunity to customize their half of the arena with pits, traps, moving platforms and the like. Any suggestions? I want cinematic, cool tricks and props that would play well to a bloodthirsty audience.
Pendulum swings with a spiked ball at the end of it, flung around by the dragonborns flailing around the arena could be entertaining. The dragonborns are used to dodging these but the PC's may need to make acrobatics checks or insight checks to avoid them. If a PC gets the bright idea to use bluff and distract a dragonborn so the spiked ball will hit them, more power to them, but otherwise the dragonborns ignore it.
Throw a rage drake in a pit, or maybe a needlefang drake swarm. Make it extra painful to fall in that pit. Or have a few guard drakes chained to a pole in the center, anyone gets too close, and they attack, but their mobility is severely limited. Something else live and hazardous in the arena keeps things interesting. Another alternative might be that the organizers have a cage of starved kobolds hidden somewhere, and at an interesting moment in the fight, could let them loose.
Dragonborns may have a few arcane tricks up their sleeves too. Maybe a pair of well disguised conduits zap you with lightning if you pass between them (perception to notice, and arcana or thievery check to recognize the trap). The smell of singed flesh should be a crowd pleaser.
