Helm of the Host

• WOTC Official Reminder Textofficial rules
  Equip — Equip [cost] ([cost]: Attach to target creature you control. Equip only as a sorcery.)

• WWizards of the Coast2018-04-27
  Official Ruling
  Any enters-the-battlefield abilities of the copied creature will trigger when the token enters the battlefield. Any "as [this creature] enters the battlefield" or "[this creature] enters the battlefield with" abilities of the chosen creature will also work.
• WWizards of the Coast2018-04-27
  Official Ruling
  If the equipped creature leaves the battlefield before the triggered ability of Helm of the Host resolves, or if there is no equipped creature, no token is created. However, if Helm of the Host leaves the battlefield while its triggered ability is on the stack, a token will be created of the creature it last equipped. If that creature has also left the battlefield, its last known information is used to determine what the token looks like.
• WWizards of the Coast2018-04-27
  Official Ruling
  If the copied creature has in its mana cost, X is considered to be 0.
• WWizards of the Coast2018-04-27
  Official Ruling
  The token isn't legendary, and this exception is copiable. If something else copies the token later, that copy also won't be legendary. If you control two or more permanents with the same name but only one is legendary, the "legend rule" doesn't apply.
• WWizards of the Coast2018-04-27
  Official Ruling
  If the copied creature is copying something else (for example, if the copied creature is a Clone), then the token enters the battlefield as whatever that creature copied.
• WWizards of the Coast2018-04-27
  Official Ruling
  The token copies exactly what was printed on the original creature and nothing else (unless that creature is copying something else or is a token; see below). It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or Auras and Equipment attached to it, or any non-copy effects that have changed its power, toughness, types, color, and so on.
• WWizards of the Coast2018-04-27
  Official Ruling
  The token gains haste indefinitely, and this effect isn't copiable. If something else copies the token later, that copy won't have haste.
• WWizards of the Coast2018-04-27
  Official Ruling
  If the copied creature is a token, the token that's created copies the original characteristics of that token as stated by the effect that created that token.

Rulings via Scryfall