(Be sure to pick up my version of Shadow Ops for LWOTC if you want more infiltration bonuses from abilities!)

- Many abilities in the aliens' trees grant bonuses to infiltration in addition to whatever else they do, and for various reasons these abilities do not identify themselves in-game. I will list them here in order of the biggest bonus to the smallest bonus:

• Apparition (Sectoid)
  
• Serpentine (Naja)
  
• Blink (Sectoid XCOM deck) and Quick Feet (Muton Prowler)
  
• Slither (Viper) and Blend (XCOM decks)
  
• Machina Puppeteer (Sectoid) and Hunt Down (Muton Hunter)
  
• Parkour (XCOM decks) and Battlespace (XCOM decks)

- The aliens themselves (mostly) have different infiltration values than human soldiers. I will list them here in approximate order of the fastest infiltrators to the slowest (this is with default gear, Squaddie rank and no utility items):

• Sectoid
  
• Sidewinder
  
• Viper
  
• Naja
  
• Muton Hunter and Muton Prowler
  
• Muton Trooper
  
• Archon
  
• Andromedon
  
• Berserker

- Upgrading a Sectoid's Psi Amp will let them infiltrate faster, just like with a Psi Operative's Psi Amp.

- Upgrading a Sidewinder's Scramgun will let them infiltrate faster, just like with a human soldier's SMG.