You can play those cards while they are exiled, and can spend mana of any color to do so
Temmet, Naktamun's Will gives +1/+1 whenever a card is drawn, Cemetery Reaper gives a static +1/+1 boost to all Zombies, and On Wings of Gold gives a +1/+1 stat boost and makes a 1/1 Zombie whenever a card leaves your graveyard
In most games of Commander, activated abilities on lands and creatures from your opponents are going to pop with regularity
Branching Bolt I like Branching Bolt a lot because for 3 mana you get to potentially kill two creatures, but for our purposes, just dealing 3 damage to the flying one is okay
Kuzco Panicked Llama, Pacha Emperors Guide, and Pluto Determined Defender are all options
They are a great way to explore a new set and generally speaking, they offer value for money