League-of-legends – Vlad’s pool and how it works against DOT

No, the order doesn't matter, both the slow and boost will be applied. However, the slow will always be more effective, so it's not necessarily worth to pop ghost while exhausted.

From http://leagueoflegends.wikia.com/wiki/Movement_speed, movement speed is calculated by:

Movement Speed = (Base Movement Speed + Flat Movement Bonuses) × (1 + Percentage Movement Bonuses) × Slow Ratio

E.g. if you have 310 base speed, your effective speed with both ghost (27% boost) and exhaust (40% slow) will be:

310 * 1.27 * 0.6 = 236.2

So the order doesn't matter, the end result is always the same. However, the slow is always more effective, because it's a ratio of the effective speed with boosts.

From the example above, normally ghosting would give you 83.7 extra speed, however, if you ghost while exhausted, you gain only 50.2.

Likewise, being exhausted normally subtracts 124 speed, but being exhausted while ghosting would subtract 157.5.

Another example; if you slow and boost yourself by an equal amount, say 20%, the net effect would be that you're slowed:

310 * 1.2 * 0.8 = 297.6

Untargetable refers to champions in a state where targeted spells cannot be cast on the untargetable champion, and nontargeted spells such as Karthus's Requiem will have no effect. Additionally, they cannot be targeted by auto attacks.

A more comprehensive list of Invulnerability:

Complete Invulnerability

These break all forms of leashes and makes the champion invulnerable to all damage.

• Shaco's Hallucinate makes him untargetable for a short time before the clone spawns.
• Zhonya's Hourglass's active ability makes your champion untargetable for two seconds.

Partial Invulnerability

Projectiles fired before the untargetability starts will have no effect. They will still take damage from DoTs such as Ignite and Malzahar's Malefic Visions and will not break leashes such as Fiddlesticks's Drain and Morgana's Soul Shackles. They will still be damaged by Zilean's Time Bomb, but not Fizz's Chum the Waters.

• Fizz's Playful makes him untargetable for 0.75 seconds or until he uses Trickster.
• Vladimir's Sanguine Pool makes him untargetable for 2 seconds.

Dashes

Projectiles (autoattacks or abilities) that are mid-flight when the character starts dashing will hit when the dash completes. They still take damage from DoTs while untargetable.

• Maokai's Twisted Advance makes him untargetable while moving to the target.
• Master Yi's Alpha Strike makes him untargetable for a short time while in flight.
• Fiora's Blade Waltz makes her untargetable for a short time while in flight.

source: http://leagueoflegends.wikia.com/wiki/Untargetable