Making a magical tattoo isn't as easy as inking the image on your skin. Depending on what it'll do you may need specific additives for the ink, to tattoo it at a certain time, specific tools, and someone with the skill and knowledge to do it at all. Each has different requirements but if you do your homework and hunt down all the supplies they're possible.
Some you may have seen in the wild (and not recognized) are:
1 Waves on the soles of the feet. Lets you walk on liquids. Usually used for water, but also works on acid, lava, oils, or any other fluid. Doesn't protect against anything but sinking though.
2 Tramp stamp of a bedroll and pillows. Creates a soft force field that supports you 6" above the ground to let you sleep comfortably on any surface.
3 Spiderwebs around the wrists and down the backs of the hands. Lets you draw silk from your hands as if you had spinnerets. You have to eat extra protein to replace what you use, double the mass of the silk you make on top of your normal diet. Or just eat the silk once you're done with it.
4 Gills, arcing behind both ears for freshwater or as slits running down the neck for saltwater. You can only have one type. Lets you breathe underwater, but you can't breathe air while it's active.
5 Hyena jaws stretching ear to ear around the mouth and across the chin. Lets you eat anything organic without trouble.
6 Ship's anchors on the back of each calf. You can't be moved against your will.
7 Moth wing eyespots on both palms. Cause terror in whoever sees them both at once.
8 Full back piece of intertwined snakes. You can shed your skin to heal wounds and regrow lost body parts. Have to eat only raw meat for a month after using it.
9 Tombstone over the heart, inscribed with your full real name and a date. You'll die at midnight on that date and not a second before no matter what happens to you.
10 Half of a chalice on the back of each hand. When you cup your hands they'll start to fill with water. It's as clean as your hands are. If you're drunk they'll fill with wine.
11 Crown of lit candles across the forehead. Glows softly, gives just enough light to see by and can't be turned off.
12 Tiny lockpicks and keys along the sides of the fingers. Lets you open locks by touch, but if you slip in a way that would break a pick it breaks your fingers.
13 Shoulder piece and upper sleeve of leaves blown on the wind. Deflects flying objects, creatures, and other projectiles away from you.
14 Circle of yew trees with gnarled roots between the shoulder blades. Tethers your soul to your body so it can't be stolen, drained, forced out, or slip away when you die.
15 Three concentric circles at the base of the skull. Negates all defenses against possession.
16 Fine chains wrapped around the throat. You can only speak the truth. Everyone recognizes what this tattoo means.
17 Fine chains wrapped around the tongue and across the inside of the mouth. What you say becomes the truth.
18 Stream of sudsy water and bubbles spiraling down the forearm. Your skin repels dirt, grime, and other filth.
19 Roaring bonfire with smoke curling around the calf. You can easily light fires using anything, no matter how wet or hard to start it should be.
20 Butterfly on the ankle. You can't become intoxicated.
21 Bouquet of yarrow and ferns on the thigh. You don't bleed when you're cut.
22 Constellations of tiny stars and suns around the eyes and across the eyelids. Lets you see lies and through illusions.
23 Burning incense at the base of the throat and plumes of smoke wrapping around the neck. Lets you speak any language but not understand them.
6 Ship's anchors on the back of each calf. You can't be moved against your will.
7 Moth wing eyespots on both palms. Cause terror in whoever sees them both at once.
8 Full back piece of intertwined snakes. You can shed your skin to heal wounds and regrow lost body parts. Have to eat only raw meat for a month after using it.
9 Tombstone over the heart, inscribed with your full real name and a date. You'll die at midnight on that date and not a second before no matter what happens to you.
10 Half of a chalice on the back of each hand. When you cup your hands they'll start to fill with water. It's as clean as your hands are. If you're drunk they'll fill with wine.
11 Crown of lit candles across the forehead. Glows softly, gives just enough light to see by and can't be turned off.
12 Tiny lockpicks and keys along the sides of the fingers. Lets you open locks by touch, but if you slip in a way that would break a pick it breaks your fingers.
13 Shoulder piece and upper sleeve of leaves blown on the wind. Deflects flying objects, creatures, and other projectiles away from you.
14 Circle of yew trees with gnarled roots between the shoulder blades. Tethers your soul to your body so it can't be stolen, drained, forced out, or slip away when you die.
15 Three concentric circles at the base of the skull. Negates all defenses against possession.
16 Fine chains wrapped around the throat. You can only speak the truth. Everyone recognizes what this tattoo means.
17 Fine chains wrapped around the tongue and across the inside of the mouth. What you say becomes the truth.
18 Stream of sudsy water and bubbles spiraling down the forearm. Your skin repels dirt, grime, and other filth.
19 Roaring bonfire with smoke curling around the calf. You can easily light fires using anything, no matter how wet or hard to start it should be.
20 Butterfly on the ankle. You can't become intoxicated.
21 Bouquet of yarrow and ferns on the thigh. You don't bleed when you're cut.
22 Constellations of tiny stars and suns around the eyes and across the eyelids. Lets you see lies and through illusions.
23 Burning incense at the base of the throat and plumes of smoke wrapping around the neck. Lets you speak any language but not understand them.
24 Coin purse on the hip. You can put small objects and coins inside for safekeeping. There's no way to see what's already inside and you have to root around to retrieve items.
25 Lines of stitching running over and around the entire body at the joints, separating it into discrete segments. You can detach parts of yourself along each line and rejoin them at will.
26 Two roses twined in briars on the sternum. Always inked in pairs. Lets you know if the other wearer's alive, where they are, and how they're feeling at all times.
27 An eye on the inside of each wrist, one open and one closed. Uncover the open eye and all attention is drawn to you, uncover the closed eye and people's awareness slides right past you.
28 Tally marks, always in a highly visible place. Starts with just one and others appear each time you do a specific action or task. The parameters are set by the tattooer and can be anything you've done once before. There's no way to tell what it is just from the marks.
29 Pi symbol on the bottom of the big toe. If you die there's a 6-in-10 chance it was a doppelganger who died, not you.
30 Ring of mushrooms around the waist. You can leave faerie at any time.
25 Lines of stitching running over and around the entire body at the joints, separating it into discrete segments. You can detach parts of yourself along each line and rejoin them at will.
26 Two roses twined in briars on the sternum. Always inked in pairs. Lets you know if the other wearer's alive, where they are, and how they're feeling at all times.
27 An eye on the inside of each wrist, one open and one closed. Uncover the open eye and all attention is drawn to you, uncover the closed eye and people's awareness slides right past you.
28 Tally marks, always in a highly visible place. Starts with just one and others appear each time you do a specific action or task. The parameters are set by the tattooer and can be anything you've done once before. There's no way to tell what it is just from the marks.
29 Pi symbol on the bottom of the big toe. If you die there's a 6-in-10 chance it was a doppelganger who died, not you.
30 Ring of mushrooms around the waist. You can leave faerie at any time.