With the help of an enemy like a Moblin and temporary invincibility, it is possible to clip through a portal linking Hyrule to Lorule and reach whatever is on the other side. The general method used to pull off this trick is the following:
In most cases, Link will then simply fall out of bounds into the void and reappear in front of the portal, but if there wall on which the portal is placed isn't too "thick", and if there is solid ground a bit lower on the other side of it, it is possible to clip through the entire wall and land on it. This is what happens in the Misery Mire area in Lorule, with the portal on the wall south of the Desert Palace boss arena.
It is also possible to clip using something else than an enemy, as shown in this video:
This technique is currently used to skip the entire Desert Palace.
Many if not all Portals have solid ground behind them, in the form of a thin straight line (believed to be no more than a few pixels wide). Link can stand on and walk along those lines to reach further into Portal walls, which can be useful for getting on top of said wall with the Tornado Rod if the Portal is facing south. (See Desert Palace Skip) Walls with Portal facing north are easier to get on top of due to the way the game is made.
The two items most commonly used to push enemies around are the Hookshot and the Sand Rod. Both of them use the same amount of energy, which is 12.5% of your total energy if you don't have the Scroll. The Sand Rod is mostly used to push the enemy over a great horizontal or vertical distance because of is large area of effect and the limited directions towards which it can be used. The Hookshot is helpful because of its capacity at shooting diagonally and precision when small pushes are required. (i.e. standing south of the enemy, aiming the Hookshot north and hitting it on its left half will move push it a bit to the right, and vice versa.) The Hookshot is also useful in taking advantage of certain enemies' attack patterns, like Spear Moblins who move away from Link while they aim. Having the Moblin moving towards the direction you want to push him, and use the Hookshot on him when he is about to throw its spear, or when close to the place you want it to be.
Most enemies, when hit by either the Sand Rod or the Hookshot, will be temporarily stunned. The duration of a stun is split into two phases: the first one where you can see stars around the enemy's head, and the second one where there are no stars, but the enemy is shaking and about to start moving again. The distinction between those two is important in order to know how to use your items properly.
It is also good to know that the duration of the stun is long enough for your energy to refill above the amount required to use either item.
Boomerang and Shield can be used as well, but since they're not obtained in a normal any%, most players will stick with the items above. If, at some point in 100%, Portal Clipping ended up being required after upgrading the items, Nice Hookshot would most likely become unusable because of its gained attack power, so Nice Boomerang and/or Shield would have to be used in its place.