Bloons Tower Defense Impersonation/Iteration Differences

The following lists of major similiarities and differences between the most recent BTD games and BTDI are described below. But mostly the differences.
 * Similarly to BTD6, towers have three different upgrade paths to upgrade to. Under normal conditions, only one of the said three paths may be upgraded past Tier II, and only two paths may be upgraded to at all. Nevertheless, the final upgrade in each upgrade path can only be beheld by one tower at a time; though, in BTDI, there are six upgrades per path and therefore six tiers, as opposed to BTD6's five. Tier V and Tier VI upgrades almost always unlock Activated Abilities, abilities that are to be activated and set on cooldown before being ready for use again.
 * Almost all towers from previous iterations (BTD4, BTD5, BTD6) return in BTDI, including Road Items such as Monkey Glue, Road Spikes, and Exploding Pineapples, towers such as Bloonchipper and Monkey Beacon (now known as Beacon Building), and supposedly unused/unreleased towers such as Dartling Gunner, Monkey Engineer, and Monkey Academy (Spike-O-Pult still remains as the 3-x-x upgrade to Dart Monkey, though the Tier IV Dart Monkey in BTD4, otherwise known as "Triple Spike-O-Pult", effectively returns as an upgrade).
 * Similarly to BTD6, Ice Monkey can freeze and pop most bloons by default. The Ice Monkey cannot pop or freeze White Bloons or Zebra Bloons under normal conditions; however, the Ice Monkey is able to freeze Lead Bloons but not pop them without the Snap Freeze upgrade.
 * Captain Cassie, C4 Charlie, Sai, and Sam from BATTD return as heroes in BTDI, each with the BTD6-esque hero level upgrade system rather than BATTD's upgrade system.
 * WIP