Cheapest priced copy (March of the Machine Commander): $2.29 at Card Kingdom, near mint, their price list as of .
Conclave Sledge-Captain 
Creature — Elephant Soldier · 4/4 · Rare · March of the Machine Commander · #123
Backup 1, backup 1, backup 1 (When this creature enters, put a +1/+1 counter on target creature. If that's another creature, it gains the following abilities until end of turn. Each backup ability triggers separately.)
Trample
Whenever this creature deals combat damage to a player, put that many +1/+1 counters on it.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $2.29 to $2.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| March of the Machine Commander | 36 | Rare | $2.29 | — |
| March of the Machine Commander | 123 | Rare | $2.99 | — |
6 rulings from Wizards of the Coast
- 14 April 2023If a backup ability causes another creature to gain abilities, the creature with backup will still have those abilities.
- 14 April 2023Backup confers only abilities that are actually printed below it. Any abilities that are gained by the permanent are ignored, including abilities gained due to a resolving spell or ability or copy effects.
- 14 April 2023If a backup ability targets the creature with backup, that creature will get +1/+1 counters, but it won’t gain additional abilities.
- 14 April 2023If the same creature is the target of more than one of Conclave Sledge-Captain’s backup abilities, it will get more than one instance of its triggered ability. Each of those triggered abilities triggers separately. If the creature deals combat damage to a player, it will get that many +1/+1 counters more than once. (It will also have trample more than once, but that’s way less interesting.)
- 14 April 2023The abilities that backup grants to the target creature are determined only once, at the time the ability triggers. They won’t change if the permanent with backup loses any abilities before the backup ability resolves.
- 14 April 2023If a permanent enters the battlefield as a copy of a card with a backup ability or a token is created that is a copy of that card, the order of the printed abilities is maintained.