Due to the high level of background magic in the world it's not not only Sorcerers that are exposed to wild magic surges. Whenever a spellcaster rolls a natural 1 or natural 20 when casting a spell they will get an additional effect to their spell. If they wish they can try to negate the result by rolling a successful Arcana DC20.

Natural 1: Use only even results (round up odd numbers, e.g. a 99 becomes a 100)

Natural 20: Use only odd resuls (round down even numbers, e.g. a 100 becomes a 99)

d100 - Effect

1-2 Roll again twice immediately.

3 - For the next minute, you can see any invisible creature if you have line of sight to it.
4 - For the next minute, all creatures appear as invisible to you even though they aren't.

5 - A modron chosen by the DM and controlled by you appears in an unoccupied space within 5 feet of you, then disappears one minute later.
6 - A hostile modron chosen and controlled by the DM appears in an unoccupied space within 5 feet of you, then disappears 1 minute later.

7 - You cast Beacon of Hope without having to keep concentration.
8 - You cast Fireball as a 3rd-level spell centered on yourself.

9 - You cast Magic Missile as a 5th-level spell.
10 - You cast Magic Missile as a 5th-level spell. The 7 darts will divide equally between all creatures in range, starting with you and going further and further out in a spiral.

11 - A pedantic poltergeist visits your backpack. Your rations are replaced with fresh ones, your clothes are cleaned and folded, and all content is sorted according to size and color.
12 - You gain the effects of the spell Reduce for 1 minute.

13 - You cast Aid.
14 - You cast Confusion centered on yourself.

15 - For the next minute, you regain 5 hit points at the start of each of your turns.
16 - For the next minute, you take 1d4 necrotic damage at the start of each of your turns. Lesser Restoration or similar spells can end the effect.

17 - You summon a Heroes' Feast.
18 - You grow red feathers all over your body and gain a flying speed of 20 feet. After 1 minute the feathers burst into flame, causing 2d10 fire damage and setting you on fire. You take 1d10 fire damage at the start of your turns until someone takes an action to douse the fire. An egg appears in the ashes.

19 - You cast Prayer of Healing.
20 - You cast Grease centered on yourself.

21 - Creatures have disadvantage on saving throws against the next spell you cast in the next minute that involves a saving throw.
22 - You have disadvantage on your saving throw against the next spell cast on you in the next minute that involves a saving throw.

23 - Your skin gets a leathery quality and your AC increases with 1 for 1 hour.
24 - Your skin turns a fluorescent shade of blue and you have disadvantage on stealth and hiding. A Remove Curse spell can end this effect.

25 - An eye appears on your forehead for the next minute. During that time, you have advantage on Wisdom (Perception) checks that rely on sight.
26 - You grow antennae that last for 24 hours. During that time, you have disadvantage on Charisma (Persuasion) checks.

27 - For the next minute, you can choose to change the casting time of any spell from 1 action to 1 bonus action.

28 - For the next minute, you can't use bonus actions.

29 - You teleport up to 60 feet to an unoccupied space of your choice that you can see.
30 - You teleport up to 60 feet in a random direction to an unoccupied space that you can see. You land prone.

31 - You cast Mass Healing Word.
32 - You are transported to another plane until the end of your next turn, after which time you return to the space you previously occupied or the nearest unoccupied space if that space is occupied. You might have brought with you a souvenir (DM's choice).

33 - Maximize the damage of the next damaging spell you cast within the next minute.
34 - Your feet grow to clown-like proportions for the next minute, making it easy to trip. Every time you start to move you need to make a Dex save DC14 or fall prone.

35 - You cast Healing Spirit without having to keep concentration.
36 - You become a d10 years older.

37 - 1d6 flumphs appear in unoccupied spaces within 60 feet of you and are controlled by you. They vanish after 1 minute.
38 - You cast Web centered on yourself.

39 - You regain 2d10 hit points.
40 - A ghostly, skeletal hand appears and clings to you. You take 1d8 necrotic damage and can’t regain hit points until the start of your next turn.

41 - Choose any number of creatures within 30 feet. For 1 hour they regain 1 hit point at the start of each of their turns (10 hit points each minute).
42 - You turn into a potted plant until the start of your next turn. While a plant, you are incapacitated and have vulnerability to all damage. If you drop to 0 hit points, your pot breaks, and your form reverts.

43 - For the next minute, you can teleport up to 20 feet as a bonus action on each of your turns.
44 - For the next minute you are affected by the spell Blink, except you will return to a random unoccupied space within 10 feet of the space you vanished from instead of a space you choose.

45 - You cast Levitate on yourself.
46 - You start to levitate 5 feet above the ground without being able to control it. You can use a sail or an anchor to try to control your movements.

47 - A unicorn controlled by the DM appears in a space within 5 feet of you, then disappears 1 minute later.
48 - A slightly annoyed rhinoceros appears in a space within 5 feet of you, then disappears 1 minute later.

49 - You gain telepathy for 1 hour. You can communicate with any creature you can see within 60 feet and they can respond if they wish. You need to share a language for the telepathy to work.
50 - You can't speak for the next minute. Whenever you try, pink bubbles float out of your mouth.

51 - A spectral shield hovers near you for the next minute, granting you a +2 bonus to AC and immunity to Magic Missile.
52 - For some reason there is a lingering odor around you for the next minute. You and any creature that starts its turn within 5 feet of you must succeed on a DC 12 Constitution saving throw or be poisoned until the start of its next turn.

53 - You can summon alcohol from your fingertips at will for the next 5d6 days.
54 - You become intoxicated by alcohol for 1d4 hours, causing disadvantage on ability checks. You are also more likely than usual to launch yourself into long expositions and rants about real or imagined slights. Can be cured by Lesser restoration or similar.

55 - Your hair looks great for the next 24 hours.
56 - Your skin becomes old and wrinkly, you start walking with a stooped posture and your hair falls out. The hair grows back within 24 hours, all other effects also gradually go away within that time. Your speed is reduced by 5 feet for the first 1 hour.

57 - The next inanimate object you touch turns into gold.
58 - For the next minute, any flammable object you touch that isn't being worn or carried by another creature bursts into flame.

59 - You regain your lowest-level expended spell slot.
60 - If you have an unused level 1 spell slot, you will use it to cast a random memorized 1st level spell on a random target.

61 - Until the next dawn, you don't need to use the verbal component in spells for them to work.
62 - For the next minute, you must shout when you speak and your body language and gestures will appear exaggerated.

63 - You can breathe water for 24 hours.
64 - You cast Silence centered on yourself.

65 - Up to three creatures you choose within 30 feet of you take 4d10 lightning damage.
66 - Three random creatures within 30 feet of you take 4d10 lightning damage.

67 - You are immune to being frightened for 1 hour.
68 - You are frightened by the nearest creature until the end of your next turn.

69 - You become invisible for 1 minute. The invisibility ends if you attack or cast a spell.
70 - Each creature within 30 feet of you becomes invisible for the next minute. The invisibility ends on a creature when it attacks or casts a spell.

71 - You gain resistance to all damage for the next minute.
72 - You gain vulnerability to frost, fire, thunder and lightning damage for the next minute.

73 - The next creature that makes a melee attack on you within 1 hour becomes poisoned for 1d4 hours.
74 - You become poisoned for 1d4 hours.

75 - You gain darkvision for the next minute. If you already have darkvision it is extended by 60 feet.
76 - You glow with bright light in a 30-foot radius for the next minute. You can't stealth or hide from creatures that can see the light. You also have disadvantage on perception checks due to being dazzled.

77 - You may cast Polymorph on a hostile creature you can see within 60 feet. If they fail the saving throw, they turn into a sheep for the spell's duration.
78 - You cast Polymorph on yourself. If you fail the saving throw, you turn into a humanoid-looking sheep for the spell's duration. Your voice sounds a bit sheep-like but you can still act as usual, and you have disadvantage on all STR and DEX based skill checks due to the unfamiliar shape.

79 - You can use your action during each of your rounds the next minute to cast this spell again at the same level without using spell slots.
80 - Once during the next minute, a hostile creature of the DM's choosing can use a reaction to copy an action you take, with the same dice rolls that you made but with a target of their choice.

81 - You can take one additional action immediately.
82 - You gain the effects of Bane for 1 minute.

83 - If may make a free ranged spell attack against a creature within 30 feet. On a hit, the target takes 3d6 necrotic damage, and you regain hit points equal to half the amount of necrotic damage dealt.
84 - You take 1d10 necrotic damage and become unable to regain hit points until the start of your next round.

85 - You cast Mirror Image.
86 - A pebble is conjured in your footwear every minute for the next hour, reducing your speed by 5 feet while wearing them.

87 - You cast Fly on yourself.
88 - You cast Fly on a random hostile creature within 60 feet of you.

89 - You become invisible for the next minute. During that time, other creatures can't hear you. The invisibility ends if you attack or cast a spell.
90 - You become deaf for 1 minute.

91 - If you die within the next minute, you immediately come back to life as if by the Reincarnate spell.
92 - The next damaging or healing spell you cast within 1 minute will have minimal effect.

93 - Your muscles grow noticeably and you have advantage on strength checks and strength saves for 24 hours.
94 - Until the end of your next round your spells have halved range if possible, otherwise halved duration if possible, otherwise halved effect if possible.

95 - You and all allies within 30 feet of you gain resistance to piercing damage for 1 minute.
96 - You and all allies within 30 feet of you gain vulnerability to piercing damage for 1 minute.

97 - For the rest of the day you are followed by nice thematic music appropriate to any cool things you are doing.
98 - You begin to hear music of a kind that really annoys you for the next minute, causing you to have disadvantage on concentration checks. Only you can hear this music.

99 - You feel refreshed and gain the effects of a long rest.
100 - You suddenly feel very tired and gain one level of exhaustion (except if you already had one).