Portals will persist after Isaac uses them or leaves the room, and will always lead to the same room.
Portals do not respect pathing rules, and can spawn on single-tile walkways and in front of doors, forcing Isaac to use them and preventing him from leaving the room through that door. This can cause a softlock depending on what door it blocks and where the portal leads.
Lil Portal bears a close resemblance to the Portal enemies, with the visual design of a Portal and the color scheme of a, well, Lil Portal.
If a portal is reencountered during the ascent, such as in a previously completed boss room, the game may crash if the destination the portal originally connected to no longer exists in the now altered floor layout.
If a portal is created in Greed Mode, there is a possibility it will take the player to the Exit room without defeating any boss.
If Lil Portal consumes a Black Heart in a Devil Room that is part of the room layout (not a reward or contents of a bag or a chest), the game crashes.
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