Town Portals
Opening up a town portal in the middle of a tricky fight is a classic way to get to safety or catch your breath. However, during the "Rite of Passage" quest this trick can result in some unwanted consequences: opening a portal in the middle of the fight against the ancients will cause them all to reset, meaning that you'll have to start the whole thing from scratch. Any portals that you open prior to starting the fight will disappear after the ancients appear.
Missing Out On Experience Points
You may have read that completing the "Rite of Passage" quest will result in a massive amount of experience points. If you've finished the fight without seeing any sort of boost in your XP, you might think that this is a glitch. On the contrary, it only means that you haven't met the level requirement for getting the XP reward. In order to get an XP bonus, you must be at least level 20 in Normal mode, Level 40 on Nightmare mode or Level 60 on Hell mode.
Multiplayer Difficulties
If you are playing in multiplayer mode, this fight poses additional limitations. Bringing a new player into the fight after it has started will reset the fight, as will any of the players leaving the fight. If a player is killed, they cannot come back to their corpse until after the fight is complete. This makes things exceptionally difficult for those who are still in the fight and must continue on a player short. Stock up on healing potions before this fight to help keep anybody from dropping out.
Technical Difficulties
Because "Diablo II" was released more than a decade ago, it may run into some unforeseen compatibility issues with your more modern computer. If you have Windows administrator privileges on your computer, try running the game in compatibility mode if you are experiencing performance problems. If you are encountering glitches or unexpected crashes during the fight, revert to an earlier save and try again. Sometimes reloading to an earlier functional point in the game can also correct any issues.