My favorite card(s) would be the Nether Warps. It is so much fun to use and so versatile. Both cards warps friendly and hostile units a short distance. The green affinity heals all units affected an the blue affinity slows them all down to walk speed. Both sides of the card requires ground presence to cast.
In pvp, you can use it to dodge important spells from your opponent like a Coldsnap or abilities like the Timeless One. It is also great to combine it with cards like cultist masters to get the Nightcrawlers right into the action. Nether Warp can also be used to get your enemy away from a well last second before it is killed. When an enemy unit is escaping with very little help, you can use the warp to get it back in range of your attacks. Because the units do not continue walking by default after they get warped, it could surprise your opponent and lead to an easy kill.
The card is also able to dodge projectiles. For example, if an Windhunter in rpve attacks your Batariel, you can warp the Batariel while the projectile is flying and the it will take no damage and does not get affected by the paralysis. In rpve, it is used to cross some walls to assists yourself or your teammates so you/they don't have to walk around an edge.
In some campaign maps, you have to defend against units that out range your Necroblasters or Church of Negation. An example could be Defending Hope or Crusade where twilight dancers attack your bases regularly. A quick warp can get them in range before they destroy your buildings.
A deck where both Nether Warps are often in the deck is the Construct rpve deck. In combination with Benevolent MO (or Dryad G) there is no debuff when you warp. This allows the possibility of the double warp which is awesome to do! To get a fast time in Bad Harvest, this trick can be used near the end and between some Stonekin lords too.
In Speedruns the card is also utilized. As mentioned before, in Bad Harvest to get to your goal faster. With the card, it is also possible to jump over some gates. A few examples are Convoy, KotG, Titans and Nightmare's End.
