Colin McLaughlin shared an interesting list of portal use complications in his 2017 post “Planescape: Keys, Portals, and Complications” (read on Tribality) that could make nice minor effects from curses or magical tricks…
Swapped. An enhancement bonus on a weapon you possess is transferred to another item in your possession for the next 24 hours. The weapon is no longer considered magic for purposes of resistances and immunities for this duration.
Interesting. You are suddenly fascinating. You have advantage on all Charisma ability checks until you complete a long rest.
Singed. You exude a faint smoky aura. You have disadvantage on Dexterity (Stealth) checks and may not benefit from invisibility or greater invisibility until you change clothes and bathe.
Scrappy. You have advantage on all saving throws against death until you roll a natural 1 on the saving throw roll. You re-roll the 1, but no longer have advantage on saving throws against death. This fades after one week if this does not occur.
Magnetic. Metal weapons are more likely to strike you. All attacks made against you with metal weapons roll 1d4 and add the result to the attack roll. This lasts until you drop to half or below of your maximum hit points for the first time after traveling through the portal.
Observant. Your eyesight is sharper than you remember. You have advantage on Intelligence (Investigation) and Wisdom (Perception) ability checks that involve sight until you imbibe alcohol or you complete three long rests.
Unlucky. Natural 2s on a 1d20 are the same as rolling a natural 1 until you receive a remove curse.
Energetic. You gain resistance to an energy type of the DMs choice. This ends after you complete three long rests, or if you become restrained or incapacitate through means other than non-magical sleep.
Winded. You have disadvantage on Strength (Athletics), Dexterity (Acrobatics), and saving throws against exhaustion until you complete a long rest.
Referential. You are proficient in Intelligence (Arcana), Intelligence (History), Intelligence (Nature), and Intelligence (Religion). If you are proficient already, you double your proficiency bonus. This lasts until you imbibe alcohol or complete three long rests.
Adorable. You have disadvantage on Charisma (Intimidation) ability checks. This is a disease and can be removed with a DC 14 Charisma saving throw during a long rest, or through magical means. You may only attempt to save once per long rest.
Empowered. Whenever you would deal damage, roll 1d4 and add the result to your damage roll. This lasts until you complete a long rest.