
Reviewed for patch 7.3b

Favorable matchup
Reviewed for patch 7.3b
Blinding Dart only cancels attacks, and Kennen's damage comes mostly from abilities: Teemo's main tool barely touches him. Kennen also has the range to answer the poke and a stun that shuts down Move Quick's mobility.
Blinding Dart only affects the target's basic attacks. Thundering Shuriken, Electrical Surge and Lightning Rush are abilities: they keep dealing damage and applying Mark of the Storm even while you're blinded.
At three marks, Kennen stuns. Move Quick gives Teemo speed and a roll to get away, but a stun stops that exit. Complete the marks with shuriken and Lightning Rush once he has spent the active.
Move Quick's passive speed is lost when Teemo takes damage from a champion. A well-timed shuriken before you go in strips that movement edge and makes it easier to finish the marks.
Trade when Teemo has used Move Quick's active or walks up to a minion. If he blinds you, don't waste time on basic attacks: use abilities during the blind and get out before he can poke you again.
As Teemo against Kennen, the blind loses value: your edge is stacked poison and positioning. Dodge the shuriken by moving behind minions and keep Move Quick's active to escape once he has two marks on you. Put mushrooms on the path he would take with Lightning Rush.

Favorable matchup
Reviewed for patch 7.3b
Cho'Gath has what Teemo least wants to see: Feral Scream silences him so he can't use Move Quick or Blinding Dart, and Carnivore gives health back on every minion kill, which takes value out of the poison poke.
Feral Scream silences enemies in a cone for a few seconds. A silenced Teemo can't activate Move Quick to run or throw Blinding Dart: he's left with basic attacks and passive speed, which he loses when he takes damage.
Carnivore restores health and mana every time Cho'Gath kills a unit. Last-hitting minions while Teemo pokes you with Toxic Shot offsets part of that damage, so his lane pressure is worth less than against a champion with no healing.
Teemo relies on Move Quick's active to get out of danger. Silenced, he can't use it: that's the moment to cast Rupture and lock in the knock-up and slow.
Go in with Feral Scream when Teemo is in range last-hitting, and follow with Rupture while the silence lasts. If he has blinded you, your basic attacks deal no damage: lean on Feral Scream and Rupture until it wears off.
Teemo has to stay out of Feral Scream's cone: if Cho'Gath spends it on the wave or misses, you get a long window to poke. Keep Blinding Dart for when Cho'Gath starts hitting you with basic attacks: blinded, his attacks deal no damage. Place mushrooms on the sides of the lane he approaches from, not just the middle.

Execution matters
Reviewed for patch 7.3b
Mordekaiser doesn't rely on attacks Blinding Dart can cancel, turns the damage he takes into a shield with Indestructible, and can pull Teemo in with Death's Grasp. It's situational: with no dash, if the pull misses, Teemo walks away and pokes again.
Obliterate and the Darkness Rise aura keep dealing damage while you're blinded, because Blinding Dart only cancels attacks. Your basic attack damage is lost during the blind, but your main combo isn't.
Indestructible stores part of the damage you take and converts it into a shield, which you can cash in for health. Toxic Shot poison and mushrooms feed that shield, so Teemo's poke doesn't translate into pure health loss.
Death's Grasp pulls enemies in an area toward you. It's your way of closing the gap against Move Quick. Use it once he has spent the roll; before that, he can step out of the area.
Look for Death's Grasp when Teemo has used Move Quick's active or walks up to last-hit. Outside those windows, farm and absorb his poke with Indestructible.
Teemo wins this matchup by keeping distance: hit and walk away before Mordekaiser can pull you, and keep Move Quick's active only for Death's Grasp. The blind does little against him; your useful damage is stacked poison and mushrooms on his path. Don't accept long fights next to him: his aura keeps hurting.