How many different phase portal challenges are there?
I am going to attempt to catalog the phase beast challenges that I am aware of. At the moment, I have a list of 14 challenges. Let me know if you know of any corrections or additions that need to be made here, and I'll add them. I've finally added the challenges added in 1.17.
Act 1 (6 Challenges)
Stay Close to Raise the Totems - Stand close to each of three totems as they rise out of the ground. Reward: One golden chest for each totem you raise
Vanquish Your Foes With Haste - Destroy as many enemies as quickly as you can (?). Reward: 1 small chest + 1 medium chest + 2 golden chests
Poison the Spider Nests - Poison several spider nests while battling the spiders that each one spawns. Reward: Gold + 1 golden chest
Ignite Braziers in Order - Light the braziers in the correct order, while battling enemies. Reward: Gold + 2 small chests + 1 medium chest
Protect the Crystals From the Goblin Hordes - Protect five ember crystals from goblin enemies. Reward: 1 small chest for the first crystal + 1 medium chest for each crystal you save (though I have yet to protect all four crystals)
Navigate the Maze - This challenge was added in version 1.17. Navigate a watery maze, collecting all three mysterious gems if you can. Reward: 3 medium chests + 1 golden chest, which is only available if you collect all 3 mysterious gems
Act 2 (7 Challenges)
Choose a Door - Battle several waves of monsters, get the dropped key, and pick one of three doors. Reward: One of the following, depending on the door you choose: (a) nothing, (b) medium amount of gold + a few chests, or (c) large amount of gold + a few large chests
Jackalbeast Gauntlet - Run the gauntlet, collecting gold and fighting Jackalbeasts as you go. Reward: Gold + 1 small chest + 2 medium chests + random items
Pirate Gauntlet - Run through the ancient pirate ships, collecting gold and battling skeleton pirates along the way. Reward: Gold + 6 small chests + 2 medium chests + random items
Slime Trio - Defeat the three giant slimes. Reward: Gold + three chests
Survive in the Arena - Survive the enemies in the arena. Reward: Gold
Dig for Buried Treasure - This challenge was added in version 1.17. Use shovels to dig for buried treasure among 20 marked places. Reward locations are random, and not all X marks have treasure (some produce a mine, some produce another shovel, and some produce nothing). Reward: 1 big + 3 small treasure chests (only available if you find their hidden locations)
Avoid the Lava - This challenge has several chests at various height levels. The goal is to get as many chests as you can while staying out of the rising lava.
Act 3 (4 Challenges)
Defeat the Troll - Defeat the champion-level troll that spawns. Reward: Gold + 2 small chests + 1 medium chest
Defeat the Witches - Defeat the two champion-level witches. Reward: Gold + 2 medium chests
Varkolyn Gauntlet - Run the gauntlet, fighting varkolyn enemies and collecting gold along the way. Reward: Gold + 5 small chests + 3 medium chests + random items
Survive the Attack - Survive an attack by a number of enemies, mines, and robots. Reward: Gold + 3 small chests + 1 medium chest
If there's a fifth challenge in act 3, I have yet to find it.